Inlay Lake is the second largest natural lake in Myanmar. Located in Shan State, in the eastern part of the country, it is a known biodiversity hotspot. The lake is negatively affected by an increasing local human population and rapid growth in both agriculture and tourism. In recent decades, several studies have listed faunistic and floristic groups in Inlay Lake, but there is still a general lack of knowledge about the aquatic macrophyte and phytoplankton community composition and abundance, and their interactions. To fill this knowledge gap, field surveys of biological and physical and chemical parameters were carried out in the period 2014–2017. They show that Inlay Lake is a shallow, clear water and calcareous lake, with nutrient concentrations indicating mesotrophic-eutrophic conditions. However, close to the shore, nutrient concentrations are generally higher, reflecting pollution from inflowing rivers, shoreline villages and floating gardens. Both the richness and abundance of aquatic macrophytes in Inlay Lake were high, with several species forming extensive stands in most of the lake over the whole survey period. Total phytoplankton and cyanobacterial biomass were low, but cyanobacteria included toxin-producing strains of Microcystis, suggesting that cyanobacterial and total phytoplankton biomass need to be kept low to avoid potentially harmful cyanobacterial blooms. Submerged macrophyte abundance and phytoplankton biomass were inversely correlated in the heavily vegetated northern lake area. Our survey suggests a great importance of the submerged macrophytes to the general water quality and the clear water state in Inlay Lake. Maintaining high macrophyte abundances should therefore be a goal in management strategies, both for Inlay Lake and other lakes in Myanmar. It is highly desirable to include macrophytes and phytoplankton in the lake monitoring in Myanmar.

Yezin Dam is a man-made reservoir located close to Yezin village in Myanmar. Its water is used for irrigation, domestic purposes and as drinking water for many urban communities in the watershed area. In recent years, increased pollution due to the concurrent development around the dam has led to water quality deterioration. No detailed study on the distribution of cyanobacteria and toxin production has been conducted so far. In order to provide insight into the extent of cyanobacteria and cyanotoxins in the dam, water samples were collected once in January 2014 for the isolation of cyanobacterial strains and eight times between March 2017 and June 2018 for the investigation of physical, chemical and biological parameters. A total of 99 phytoplankton taxa belonging to 50 genera were recorded from Yezin Dam. Microscopic examination showed that a Dolichospermum sp. was the dominant cyanobacterium followed by small numbers of Microcystis, and Raphidiopsis raciborskii in all samples throughout the sampling period. 15 isolated cyanobacterial strains were classified morphologically and phylogenetically as Dolichospermum smithii, R. raciborskii and Microcystis and tested for microcystins (MCs), cylindrospermopsins (CYNs), saxitoxins (STXs) and anatoxins (ATXs) by liquid chromatography-tandem mass spectrometry (LC–MS/MS) and enzyme-linked immunosorbent assay (ELISA). The toxin analysis of all isolated Dolichospermum strains by ELISA and LC–MS did not indicate the presence of ATXs, STXs, CYNs nor MCs. Four of the five isolated Raphidiopsis strains produced CYN and deoxyCYN. One of the isolated Microcystis strains (AB2017/08) from Yezin Dam produced 22 MC congeners. Concentrations of 0.12 μg L−1 CYNs and 0.34 μg L−1 MCs were also found in an environmental sample from Yezin Dam by ELISA. The potential therefore exists for the use of untreated water from Yezin Dam to cause harmful effects on humans, domestic and wild animals.

Meiktila Lake is a shallow reservoir located close to Meiktila city in central Myanmar. Its water is used for irrigation, domestic purposes and drinking water. No detailed study of the presence of cyanobacteria and their potential toxin production has been conducted so far. To ascertain the cyanobacterial composition and presence of cyanobacterial toxins in Meiktila Lake, water samples were collected in March and November 2017 and investigated for physico-chemical and biological parameters. Phytoplankton composition and biomass determination revealed that most of the samples were dominated by the cyanobacterium Raphidiopsis raciborskii. In a polyphasic approach, seven isolated cyanobacterial strains were classified morphologically and phylogenetically as R. raciborskii, and Microcystis spp. and tested for microcystins (MCs), cylindrospermopsins (CYNs), saxitoxins and anatoxins by enzyme-linked immunosorbent assay (ELISA) and liquid chromatography–mass spectrometry (LC–MS). ELISA and LC–MS analyses confirmed CYNs in three of the five Raphidiopsis strains between 1.8 and 9.8 μg mg−1 fresh weight. Both Microcystis strains produced MCs, one strain 52 congeners and the other strain 20 congeners, including 22 previously unreported variants. Due to the presence of CYN- and MC-producing cyanobacteria, harmful effects on humans, domestic and wild animals cannot be excluded in Meiktila Lake.

Ministry of Environmental Conservation and Forestry, Myanmar; Norwegian Ministry of Foreign Affairs, Norway