Freshwater ecosystems, though covering less than 1% of Earth's surface, harbor around 10% of all species. Pressures like pollution, water extraction, and habitat loss can exhibit complex interactions in their effects on freshwater biodiversity. Understanding the effects of these pressures on ecosystem services and functions of freshwater systems is crucial for effective environmental policies, and asks for availability of species data. We therefore compiled European monitoring data on macroinvertebrates from European, national, and regional biomonitoring and analysed their representativeness with respect to river size, land use as well as their suitability to derive biodiversity trends. The dataset consists of over 2.3 million macroinvertebrate abundance records from 2010 to 2015, spanning 28 European countries. Geographically, data are concentrated in central Europe and England and are not evenly representative across space or river types. They vary regarding reporting units, general sampling methods, and taxonomic levels (mainly species level). These differences hamper European-scale biodiversity comparisons. The WFD primarily focuses on assessing the "ecological status" of water bodies, which can be achieved using a menu of methods and many biodiversity research questions require improvements in harmonization of taxonomic resolutions and in method standardization to enable accurate transnational comparisons. This study emphasizes the need for improved European coordination and support in collecting, validating, exchanging, and sharing freshwater biodiversity data to enable meaningful comparisons among countries. It also delivers an open-access database that enables analyses of trends and ecological scenario development, offering further opportunities to enhance freshwater biodiversity conservation and management.

ABSTRACT Freshwater ecosystems are threatened by increasing climate extremes including drought, which interacts with human pressures to drive biodiversity loss across spatial scales. River communities are considered resilient to droughts, but this characterization is based on short‐term, small‐scale studies. Moreover, drought resilience is increasingly compromised by human pressures. We used an unprecedented long‐term, large‐scale dataset spanning 359 perennial and near‐perennial river sites in south England sampled over 8–30 years to characterize ecological responses to multiple droughts and interacting human pressures, during a period of improving water quality. We determined how drought characteristics (including duration, magnitude, frequency, and spatial extent) and human pressures (including flow alteration and water quality) interact to influence aquatic invertebrate community resistance and resilience to droughts, including identification of persistent shifts in community composition. Although communities recovered on average within 1.5 years after 83% of droughts, those at 47% of sites experienced ≥ 1 long‐term, drought‐related compositional shift, challenging the paradigm of their resilience. Persistent shifts increased with drought duration and decreased with drought frequency, while anthropogenic flow reductions and lower oxygen concentrations altered community resistance and resilience to drought. Communities also experienced temporal drift (i.e., gradual compositional change) concurrent with improvements in water quality, and shifts were similarly frequent in drought and non‐drought periods. Pollution‐sensitive taxa often characterized communities following drought, indicating that these disturbance events can reset communities, allowing sensitive taxa to benefit from improved water quality. Our results also confirm the key effect of drought severity and frequency on long‐term community responses and the impacts of water abstraction and pollution on these responses. As drought severity increases in many global regions, our results could inform management actions that mitigate the ecological impacts of droughts in rivers exposed to multiple pressures.

ABSTRACT Terrestrial arthropods form biodiverse communities that support the structure and functioning of riparian ecosystems and are shaped by local to large‐scale connectivity in three dimensions. In particular, river characteristics such as size and flow permanence are likely to influence lateral cross‐channel connectivity, but how such temporally variable natural barriers shape riparian communities is rarely quantified. We tested the connectivity of communities comprising a diverse family of largely ground‐dwelling terrestrial arthropods (ground beetles, Coleoptera: Carabidae) by repeatedly sampling parallel riparian zones along rivers spanning a gradient of flow permanence during flow recession—when declining water levels theoretically reduced the barrier separating communities on left and right banks. We quantified cross‐channel connectivity by comparing left–right bank community dissimilarity using Sørensen β diversity and null‐model‐derived z‐scores, distinguishing species capable of flight from those with limited or no flight ability. Communities in parallel riparian zones were similar along the gradient, suggesting that river channels represent comparably weak barriers to cross‐channel movement regardless of water levels. In particular, species capable of flight were unaffected by in‐channel conditions, whereas the cross‐channel comparability of assemblages with limited flight abilities increased as flows declined. The replacement of water‐associated species by generalists as flows declined suggests that access to water as a resource may be more important than the barrier posed by water in structuring riparian ground beetle communities. To balance access to key resources, such as water, with the connectivity communities require for long‐term resilience, management actions should seek to mitigate climate‐driven shifts in spatiotemporal extent of river drying.

Temporary streams are impacted by climate change and other anthropogenic pressures, but fluctuating water levels complicate ecological assessments. Terrestrial invertebrate communities may enable dry-phase assessments, but their sampling can be resource intensive. We assessed diurnal variability in the capacity of two methods (hand searching and pitfall trapping) to rapidly characterise terrestrial invertebrate assemblages and their responses to environmental conditions when channels are dry. The methods provided comparable estimates of richness and abundance at any time of day (i.e., morning, midday and evening), and among sites with different dry-phase durations, air temperatures and proportions of fine sediment. Differences in taxonomic assemblage composition were detected among sites with differing dry-phase durations, air temperatures and proportions of fine sediment, suggesting that the effects of natural and human-influenced environmental stressors can be detected despite intermittence. Assemblage composition differed between methods, but not among times of day, suggesting diurnal activity patterns need not hinder assemblage characterisation in dry streams. Taxon-specific preferences for dry-phase duration, silt and sand suggest that biomonitoring indices which distinguish the influence of drying from human impacts could be developed. Monitoring over shorter periods may provide managers, regulators and citizen scientists with opportunities to increase the representation of terrestrial assemblages in ecosystem health assessments for temporary streams.

Nature-based Solutions (NbS) are ways in which the environment can be modified or managed to restore, protect, or mimic natural processes and functions. It has been suggested that NbS can enhance the resilience of the freshwater environment to the impacts of climate change and other human pressures such as diffuse agricultural pollution. Overall, evidence from catchments in temperate climates shows that NbS can positively influence a wide range of hydrological and ecological properties and processes, providing beneficial outcomes for the management of hydrological extremes (floods and low flows), water quality, and biodiversity. However, NbS also have the potential to result in disbenefits, trade-offs or unintended consequences when implemented in unsuitable settings, or with ineffective management of interventions. In some cases, studies were unable to fully determine the effectiveness of NbS due to insufficient monitoring. The provision of benefits or disbenefits from some NbS can vary temporally, with influences such as rainfall and flow conditions playing a role in the outcomes that can be achieved. Despite an increase in the publication of studies examining the effects of NbS, significant knowledge gaps remain. In particular, monitoring over longer timescales and in different catchment settings is needed to evaluate the benefits and disbenefits of NbS to better inform their future implementation and management. Evidence gaps are a known barrier to the uptake of NbS. We find that conflicting land-use priorities are also an issue. Knowledge gaps and wider socio-economic barriers need to be addressed to achieve optimal outcomes from NbS.

The past 50 years have seen biomonitoring emerge as an essential means of generating the knowledge needed to inform protection and restoration of freshwater ecosystems. Despite the successes of biomonitoring, most freshwater ecosystems remain unmonitored. Moreover, degradation of freshwaters continues at a rapid rate with new threats and novel stressors emerging that are difficult to assess using existing techniques. New technologies and techniques have been developed to improve biomonitoring, but application has been slow and integration with existing approaches is often problematic. Clearly, freshwater biomonitoring faces many important challenges that must be addressed to meet management needs of the coming decades. We identify Grand Challenges facing freshwater biomonitoring with the aim of encouraging research and practice to address these challenges. We asked 256 biomonitoring scientists from around the globe to identify what they considered the most important challenges. From their submissions we established five Grand Challenges and 18 associated subchallenges. For each Grand Challenge, we outline the current state of biomonitoring practice and suggest promising pathways and approaches to address them. By identifying and describing these challenges, we strive to position freshwater biomonitoring to take advantage of emerging opportunities and enhance its capacity to meet current and future management needs.

Intermittent rivers represent more than half of the length of the global river network, and their extent is predicted to increase. Although flow intermittence is a natural phenomenon, it is exacerbated by the combined and interacting effects of climate change and anthropogenic pressures. This increasing intermittence represents a major threat to freshwater biodiversity and highlights the pressing need for indices that can assess the responses of freshwater biota to drying events. However, most such indices remain untested beyond their region of origin, limiting their widespread use. We addressed this gap by testing the capacity of two macroinvertebrate-based indices that respond to flow intermittence (the drought effect of habitat loss on invertebrates [DEHLI] index and the monitoring intermittent streams index [MIS-index]), developed and evaluated in United Kingdom, to distinguish between perennial and intermittent river sites in Italy. Scores for both indices and index-derived richness metrics (i.e., the taxa richness of groups of environmental association classified by the indices) were higher at perennial than at intermittent sites. Among index-derived richness metrics, only those including rheophilic taxa were lower at intermittent sites, whereas others were comparable at perennial and intermittent sites. Our results suggest that both indices have the potential for use beyond their original region of development, with a better performance of the DEHLI index due to its family-level taxonomic resolution. However, their responsiveness could be enhanced by regional adaptation to increase the pool of scoring taxa. In addition, the development of conceptual frameworks predicting assemblage composition in intermittent rivers across different biogeographical regions could guide the future development of new indices for flow intermittence.

The chalk streams of the UK are globally rare, strongly intermittent in their upper reaches, and highly valued for their biodiversity and historical provision of water resources. Recent projections of river flows and groundwater levels under climate change in the UK, coupled to existing statistical models of hydrological state, enable the projection of spatiotemporal intermittence patterns into the near- and far-future. Catchments were selected for the study based on the availability of data and the performance of statistical models in the historical period. Cumulative logit models, previously trained on historical data, were used in conjunction with state-of-the-art ensemble projections of future river flows and groundwater levels to simulate future hydrological state at multiple sites along chalk streams in the south-east of England. Heatmaps visualise spatiotemporal variations in state, and intermittence metrics quantify the variability. The results show projected increases in drying into the future, both temporally, with greater duration of drying, and spatially, with intermittence extending downstream. Some sites are likely to alter substantially, for example, on the river Chess with notable decreases in modelled flow permanence projected, from 75% in the baseline period (2005-2020) to 25% in the far future (2065-2080). This research provides quantifiable spatiotemporal dynamics of intermittence, informing water resource decisions, drought management and engagement activities on these high-profile streams. The methods developed are adaptable for transfer to other catchments for which spatiotemporal mapping of intermittence patterns and future projections of driving variables exist.

Drying river networks include non-perennial reaches that cease to flow or dry, and drying is becoming more prevalent with ongoing climate change. Biodiversity responses to drying have been explored mostly at local scales in a few regions, such as Europe and North America, limiting our ability to predict future global scenarios of freshwater biodiversity. Locally, drying acts as a strong environmental filter that selects for species with adaptations promoting resistance or resilience to desiccation, thus reducing aquatic α-diversity. At the river network scale, drying generates complex mosaics of dry and wet habitats, shaping metacommunities driven by both environmental and dispersal processes. By repeatedly resetting community succession, drying can enhance β-diversity in space and time. To investigate the transferability of these concepts across continents, we compiled and analyzed a unique dataset of 43 aquatic invertebrate metacommunities from drying river networks in Europe and South America. In Europe, α-diversity was consistently lower in non-perennial than perennial reaches, whereas this pattern was not evident in South America. Concomitantly, β-diversity was higher in non-perennial reaches than in perennial ones in Europe but not in South America. In general, β-diversity was predominantly driven by turnover rather than nestedness. Dispersal was the main driver of metacommunity dynamics, challenging prevailing views in river science that environmental filtering is the primary process shaping aquatic metacommunities. Lastly, α-diversity decreased as drying duration increased, but this was not consistent across Europe. Overall, drying had continent-specific effects, suggesting limited transferability of knowledge accumulated from North America and Europe to other biogeographic regions. As climate change intensifies, river drying is increasing, and our results underscore the importance of studying its effects across different regions. The importance of dispersal also suggests that management efforts should seek to enhance connectivity between reaches to effectively monitor, restore and conserve freshwater biodiversity.

Temporary streams dominate global river networks and thus often occur in catchments dominated by agricultural land uses. Drying and agriculture can exert similar stressors on aquatic communities, for example, by decreasing dissolved oxygen concentrations and increasing fine sediment deposition. However, little is known about the effects of agriculture in driving taxonomic and trait variability in temporary stream communities. Therefore, we compared the effects of agricultural land use on variability in taxonomic and functional macroinvertebrate communities in temporary and perennial streams. We used 98 macroinvertebrate samples collected from sites with perennial (n = 49) and temporary (n = 49) flow in southern England. We quantified the spatial extent of agriculture surrounding each site, assigned samples to high (n = 62) and low (n = 36) agricultural land use categories, and tested whether variability in community composition differed between perennial and temporary reaches and between high and low agricultural categories. We also tested whether the occurrence of temporary stream specialist species was influenced by agriculture. Regardless of agricultural land use, temporary reach communities were more variable than those in perennial reaches, suggesting that drying is a bigger influence than agriculture on stream communities. Within temporary reaches, communities were comparably variable regardless of agriculture, whereas agriculture increased variability among perennial reach communities. The occurrence of temporary stream specialists was unaffected by agriculture. Our results suggest that tolerance of drying by temporary stream communities confers tolerance of agriculture. This co-tolerance of drying and agriculture may occur because temporary stream communities typically comprise species that experience agriculture and drying as comparable pressures. These species include temporary stream specialists that tolerate a wide range of environmental conditions, including drying. Although temporary stream communities and their specialist species may be co-tolerant of drying and agriculture, these and other human pressures are intensifying, with potentially detrimental impacts on their long-term stability.

Landscape rewilding has the potential to help mitigate hydrological extremes by allowing natural processes to function. Our systematic review assessed the evidence base for rewilding-driven mitigation of high and low flows. The review uncovers a lack of research directly addressing rewilding, but highlights research in analogue contexts which can, with caution, indicate the nature of change. There is a lack of before-after studies that enable deeper examination of temporal trajectories and legacy effects, and a lack of research on the scrub and shrubland habitats common in rewilding projects. Over twice as much evidence is available for high flows compared to low flows, and fewer than one third of studies address high and low flows simultaneously, limiting our understanding of co-benefits and contrasting effects. Flow magnitude variables are better represented within the literature than flow timing variables, and there is greater emphasis on modeling for high flows, and on direct measurement for low flows. Most high flow studies report a mitigating effect, but with variability in the magnitude of effect, and some exceptions. The nature of change for low flows is more complex and suggests a higher potential for increased low flow risks associated with certain trajectories but is based on a very narrow evidence base. We recommend that future research aims to: capture effects on both high and low flow extremes for a given type of change; analyze both magnitude and timing characteristics of flow extremes; and examine temporal trajectories (before and after data) ideally using a full before-after-control-impact design.

Drought is an increasing risk to the biodiversity within rivers-ecosystems which are already impacted by human activities. However, the long-term spatially replicated studies needed to generate understanding of how anthropogenic stressors alter ecological responses to drought are lacking. We studied aquatic invertebrate communities in 2500 samples collected from 179 sites on rivers emerging from England's chalk aquifer over three decades. We tested two sets of alternative hypotheses describing responses to and recovery from drought in interaction with human impacts affecting water quality, fine sediment, water temperature, channel morphology, flow and temporal change in land use. We summarized communities using taxa richness, an index indicating tolerance of anthropogenic degradation (average score per taxon, ASPT) and deviation from the average composition. Responses to drought were altered by interactions with human impacts. Poor water quality exacerbated drought-driven reductions in taxa richness. Drought-driven deviations from the average community composition were reduced and enhanced at sites impacted by flow augmentation (e.g. effluent releases) and flow reduction (e.g. abstraction), respectively. Human impacts altered post-drought recovery. Increases in richness were lower at sites impacted by water abstraction and higher at sites with augmented flows, in particular as recovery trajectories extended beyond 3 years. ASPT recovered faster at sites that gained woodland compared to urban land, due to their greater recovery potential, that is, their lower drought-driven minimum values and higher post-drought maximum values. Synthesis and applications. We show that communities in river ecosystems exposed to human impacts-in particular poor water quality, altered flow volumes and land use change-are particularly vulnerable to drought. These results provide evidence that management actions taken to enhance water quality, regulate abstraction and restore riparian land use could promote ecological resilience to drought in groundwater-dominated rivers such as globally rare chalk streams and other rivers of the Anthropocene, as they adapt to a future characterized by increasing climatic extremity. We show that communities in river ecosystems exposed to human impacts-in particular poor water quality, altered flow volumes and land use change-are particularly vulnerable to drought. These results provide evidence that management actions taken to enhance water quality, regulate abstraction and restore riparian land use could promote ecological resilience to drought-in groundwater-dominated rivers such as globally rare chalk streams and other rivers of the Anthropocene-as they adapt to a future characterized by increasing climatic extremity.image

Physical habitat modification is one of the main pressures affecting river environments, impacting their ecosystem health and compromising their ability to adapt to the effects of climate change. Addressing the impacts of physical modification through reinvigorating natural processes has become a globally established river restoration technique. Here, we appraised such an approach by assessing ecological responses to a weir removal project on an English groundwater-dominated 'chalk' stream. Using a Before-After-Control-Impact (BACI) approach, we found that 3 years post-restoration the macroinvertebrate communities are moving towards those of the target community both in terms of structural complexity (e.g., taxonomic composition) and functional integrity (e.g., trait composition). The progress is ongoing and has occurred alongside wider catchment improvements. Our results indicate that ecological responses to passive restoration undertaken on low energy streams, such as chalk streams, may be gradual, and thus longer-term assessment is needed to fully appraise ecological recovery. We highlight the importance of a BACI approach to understand the local responses to restoration in a catchment context. Our findings also provide further evidence highlighting complementary ecological information provided by assessing taxonomic and functional properties concurrently in post-project appraisals. A better understanding of ecological recovery times should be incorporated into future restoration planning. Such evidence would help develop robust assessments over appropriate timescales, increasing the likelihood of accurately and effectively appraising restoration project success, and helping to build support to increase the scale and pace of restoration actions needed to address biodiversity loss.

The chalk streams of the UK are globally rare, strongly intermittent in their upper reaches, and highly valued for their biodiversity and historical provision of water resources. Recent projections of river flows and groundwater levels under climate change in the UK, coupled to existing statistical models of hydrological state, enable the projection of spatiotemporal intermittence patterns into the near- and far-future.   Catchments were selected for the study based on the availability of data and the performance of statistical models in the historical period.  Cumulative logit models, previously trained on historical data, were used in conjunction with state-of-the-art ensemble projections of future river flows and groundwater levels to simulate future hydrological state at multiple sites along chalk streams in the south-east of England.  Heatmaps visualise spatiotemporal variations in state, and intermittence metrics quantify the variability.    The results show projected increases in drying into the future, both temporally, with greater duration of drying, and spatially, with intermittence extending downstream.  Some sites are likely to alter substantially, for example, on the river Chess with notable decreases in modelled flow permanence projected, from 75% in the baseline period (2005-2020) to 25% in the far future (2065-2080).  This research provides quantifiable spatiotemporal dynamics of intermittence, informing water resource decisions, drought management and engagement activities on these high-profile streams.  The methods developed are adaptable for transfer to other catchments for which spatiotemporal mapping of intermittence patterns and future projections of driving variables exist.

Rising water temperatures in rivers due to climate change are already having observable impacts on river ecosystems. Warming water has both direct and indirect impacts on aquatic life, and further aggravates pervasive issues such as eutrophication, pollution, and the spread of disease. Animals can survive higher temperatures through physiological and/or genetic acclimation, behavioral and phenological change, and range shifts to more suitable locations. As such, those animals that are adapted to cool-water regions typically found in high altitudes and latitudes where there are fewer dispersal opportunities are most at risk of future extinction. However, sub-lethal impacts on animal physiology and phenology, body-size, and trophic interactions could have significant population-level effects elsewhere. Rivers are vulnerable to warming because historic management has typically left them exposed to solar radiation through the removal of riparian shade, and hydrologically disconnected longitudinally, laterally, and vertically. The resilience of riverine ecosystems is also limited by anthropogenic simplification of habitats, with implications for the dispersal and resource use of resident organisms. Due to the complex indirect impacts of warming on ecosystems, and the species-specific physiological and behavioral response of organisms to warming, predicting how river ecosystems will change in the future is challenging. Restoring rivers to provide connectivity and heterogeneity of conditions would provide resilience to a range of expected co-occurring pressures, including warming, and should be considered a priority as part of global strategies for climate adaptation and mitigation.

Climate change is interacting with water resource pressures to alter the frequency, severity and spatial extent of drought, which can thus no longer be considered a purely natural hazard. Although particularly severe ecological impacts of drought have occurred in drylands, its effects on temperate ecosystems, including rivers, are also considerable. Extensive research spanning a diverse range of UK rivers offers an opportunity to place the effects of past drought in the context of intensifying climate change and to examine the likely effects of future drought in a typically cool, wet country. Here, drought manifests instream as deficits in surface water, modified flow velocities, and-increasingly-partial or complete drying of previously perennial and naturally non-perennial reaches. As a result, drought causes declines in the taxonomic and functional biodiversity of freshwater communities including microorganisms, algae, plants, invertebrates and fish, altering ecological processes and associated benefits to people. Although freshwater communities have typically recovered quickly after previous UK droughts, an increase in drought extremity may compromise recovery following future events. The risk of droughts that push ecosystems beyond thresholds to persistent, species-poor, functionally simplified states is increasing. Research and monitoring are needed to enable timely identification of rivers approaching such thresholds and thus to inform interventions that pull these ecosystems back from the brink. Management actions that support natural flow regimes and promote natural processes that diversify instream habitats, including drought refuges, are also crucial to support biodiversity within functional river ecosystems as they adapt to a changing world. This article is categorized under: Water and Life > Nature of Freshwater Ecosystems Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness

Freshwater macroinvertebrates are a diverse group and play key ecological roles, including accelerating nutrient cycling, filtering water, controlling primary producers, and providing food for predators. Their differences in tolerances and short generation times manifest in rapid community responses to change. Macroinvertebrate community composition is an indicator of water quality. In Europe, efforts to improve water quality following environmental legislation, primarily starting in the 1980s, may have driven a recovery of macroinvertebrate communities. Towards understanding temporal and spatial variation of these organisms, we compiled the TREAM dataset (Time seRies of European freshwAter Macroinvertebrates), consisting of macroinvertebrate community time series from 1,816 river and stream sites (mean length of 19.2 years and 14.9 sampling years) of 22 European countries sampled between 1968 and 2020. In total, the data include >93 million sampled individuals of 2,648 taxa from 959 genera and 212 families. These data can be used to test questions ranging from identifying drivers of the population dynamics of specific taxa to assessing the success of legislative and management restoration efforts.

Owing to a long history of anthropogenic pressures, freshwater ecosystems are among the most vulnerable to biodiversity loss 1 . Mitigation measures, including wastewater treatment and hydromorphological restoration, have aimed to improve environmental quality and foster the recovery of freshwater biodiversity 2 . Here, using 1,816 time series of freshwater invertebrate communities collected across 22 European countries between 1968 and 2020, we quantified temporal trends in taxonomic and functional diversity and their responses to environmental pressures and gradients. We observed overall increases in taxon richness (0.73% per year), functional richness (2.4% per year) and abundance (1.17% per year). However, these increases primarily occurred before the 2010s, and have since plateaued. Freshwater communities downstream of dams, urban areas and cropland were less likely to experience recovery. Communities at sites with faster rates of warming had fewer gains in taxon richness, functional richness and abundance. Although biodiversity gains in the 1990s and 2000s probably reflect the effectiveness of water-quality improvements and restoration projects, the decelerating trajectory in the 2010s suggests that the current measures offer diminishing returns. Given new and persistent pressures on freshwater ecosystems, including emerging pollutants, climate change and the spread of invasive species, we call for additional mitigation to revive the recovery of freshwater biodiversity.

There is mounting evidence that terrestrial arthropods are declining rapidly in many areas of the world. It is unclear whether freshwater invertebrates, which are key providers of ecosystem services, are also declining. We addressed this question by analysing a long-term dataset of macroinvertebrate abundance collected from 2002 to 2019 across 5009 sampling sites in English rivers. Patterns varied markedly across taxonomic groups. Within trophic groups we detected increases in the abundance of carnivores by 19% and herbivores by 14.8%, while we estimated decomposers have declined by 21.7% in abundance since 2002. We also found heterogeneity in trends across rivers belonging to different typologies based on geological dominance and catchment altitude, with organic lowland rivers having generally higher rates of increase in abundance across taxa and trophic groups, with siliceous lowland rivers having the most declines. Our results reveal a complex picture of change in freshwater macroinvertebrate abundance between taxonomic groups, trophic levels and river typologies. Our analysis helps with identifying priority regions for action on potential environmental stressors where we discover macroinvertebrate abundance declines.

Europe has experienced a substantial increase in non-indigenous crayfish species (NICS) since the mid-20th century due to their extensive use in fisheries, aquaculture and, more recently, pet trade. Despite relatively long invasion histories of some NICS and negative impacts on biodiversity and ecosystem functioning, large spatio-temporal analyses of their occurrences are lacking. Here, we used a large freshwater macroinvertebrate database to evaluate what information on NICS can be obtained from widely applied biomonitoring approaches and how usable such data is for descriptions of trends in identified NICS species. We found 160 time-series containing NICS between 1983 and 2019, to infer temporal patterns and environmental drivers of species and region-specific trends. Using a combination of meta-regression and generalized linear models, we found no significant temporal trend for the abundance of any species (Procambarus clarkii, Pacifastacus leniusculus or Faxonius limosus) at the European scale, but identified species-specific predictors of abundances. While analysis of the spatial range expansion of NICS was positive (i.e. increasing spread) in England and negative (significant retreat) in northern Spain, no trend was detected in Hungary and the Dutch-German-Luxembourg region. The average invasion velocity varied among countries, ranging from 30 km/year in England to 90 km/year in Hungary. The average invasion velocity gradually decreased over time in the long term, with declines being fastest in the Dutch-German-Luxembourg region, and much slower in England. Considering that NICS pose a substantial threat to aquatic biodiversity across Europe, our study highlights the utility and importance of collecting high resolution (i.e. annual) biomonitoring data using a sampling protocol that is able to estimate crayfish abundance, enabling a more profound understanding of NICS impacts on biodiversity.