The Metropolitan Water District of Southern California is a regional wholesaler and the largest supplier of treated water in the United States. The name is usually shortened to "Met," "Metropolitan," or "MWD." It is a cooperative of fourteen cities, eleven municipal water districts, and one county water authority, that provides water to 19 million people in a 5,200-square-mile (13,000 km2) service area. It was created by an act of the California Legislature in 1928, primarily to build and operate the Colorado River Aqueduct. Metropolitan became the first (and largest) contractor to the State Water Project in 1960.Metropolitan owns and operates an extensive range of capital facilities including the Colorado River Aqueduct which runs from an intake at Lake Havasu on the California-Arizona border to its endpoint at the Lake Mathews reservoir in Riverside County. It also imports water supplies from northern California via the 444-mile (715 km) California Aqueduct as a contractor to the State Water Project. In 1960, Metropolitan became the first (and largest) contractor to the State Water Project. Metropolitan's extensive water system includes three major reservoirs, six smaller reservoirs, 830 miles (1,340 km) of large-scale pipes, about 400 connections to member agencies, 16 hydroelectric facilities and five water treatment plants.It serves parts of Los Angeles, Orange, San Diego, Riverside, San Bernardino and Ventura counties. The district covers the coastal and most heavily populated portions of Southern California; however large portions of San Diego, San Bernardino and Riverside counties are located outside of its service area.The Metropolitan headquarters is in downtown Los Angeles, adjacent to historic Union Station.
Abstract Consumptive use of freshwater is of concern in many estuarine ecosystems, and various frameworks have been used to prescribe environmental flows to benefit native species. However, few of these frameworks explicitly examine the potential trade‐offs between socioeconomic and conservation‐oriented values. This is exemplified in California, USA, where freshwater management has been an area of focus and controversy. Operations of numerous reservoirs and water diversion facilities distributed throughout the state, while critical for economic and public health benefits, have contributed to the decline of many native species. The endangered delta smelt (Hypomesus transpacificus) is endemic to the Sacramento‐San Joaquin Delta, the heart of California's complex water conveyance system. To aid recovery of delta smelt, fall‐timed freshwater pulse flows were implemented, which require water to be either released from reservoirs, or made unavailable to export for consumptive uses. Previous research has indicated that the effectiveness of the current pulse flow action could be improved by reconsidering the timing and magnitude; however, uncertainties in the predicted fish response to flow pulses may hinder decision‐making about flow management. Using a water resource planning model, different iterations of an individual‐based life cycle model, and decision analysis tools, we assessed the importance of sources of uncertainty to hypothetical flow management decisions, including uncertainty surrounding the predicted responses in delta smelt population growth rates, and variability of decision‐maker's values. We found both the choice of which (if any) flow action to take for delta smelt, and the expected value of further research, depended on how decision‐makers weight the delta smelt and water supply objectives. There was expected value of information (VOI) only if a decision‐maker weighted the delta smelt objective ≥0.59, and within this range, research to improve estimates of changes in delta smelt prey items related to flow actions could be prioritized over other sources of uncertainty to improve outcomes of decision‐making. Our study demonstrates how uncertainty, even if large, may not be equally relevant to different decision‐makers (e.g., with different agency missions), and how VOI analysis can be used to guide management in an overallocated water system such as California.
Chinook Salmon (Oncorhynchus tshawytscha) populations in the Sacramento-San Joaquin Delta have declined likely due to multiple environmental stressors. Among the candidate factors contributing to these declines are habitat alteration, hydrologic modification, and pesticide exposure which can disrupt salmonid physiology and behavior. This study assessed pesticide exposure by whole-body residue analysis of hatchery-origin field-caught juvenile Chinook Salmon during their early ocean outmigration (2022-2025) to evaluate how residency duration, migration route, and release origin influence contaminant accumulation. In parallel, juvenile Chinook Salmon were exposed in cages at five sites within migration pathways to confirm pesticide accumulation and compare residues. Target analytes, including the insecticides bifenthrin, fipronil, 4,4'-dichlorodiphenyltrichloroethane (DDT) and common degradation products 4,4'-dichlorodiphenyldichloroethylene (DDE), 4,4'-dichlorodiphenyldichloroethane (DDD), fipronil sulfone, fipronil sulfide, and fipronil desulfinyl were quantified in whole-body homogenates. Consistent pesticide exposure was observed in the field-caught salmon, with DDE residues being found in all salmon samples as high as 4.80 nmol/g lipid (average = 0.671 nmol/g lipid), and bifenthrin residues were detected in most samples (91%) as high as 0.43 nmol/g lipid (average = 0.046 nmol/g lipid). DDT, DDD, fipronil, and fipronil degradation products were detected less frequently and at lower concentrations, indicating additional, but lower exposure (23% DDT + DDD; 8.5% fipronil (sum)). Pesticide residues increased significantly with residency time, and a six-fold increase in bifenthrin and four-fold increase in DDE were observed. A multivariate analysis indicated that the route of outmigration was also a significant predictor for bifenthrin and DDE accumulation. Cage-exposed salmon deployed for 2 weeks at five Delta sites showed consistent accumulation, with a similar residue pattern as the field-caught salmon. These results demonstrate that pesticide accumulation in juvenile Chinook Salmon during outmigration is driven by the combined effects of residency duration, migration timing, and watershed characteristics, with implications for contaminant exposure and risk assessments in the Delta ecosystem.
Hydrophobic organic contaminants (HOCs) pose risk to aquatic organisms at high concentrations and have been implicated in the declining health of the endangered fish species, Delta smelt (Hypomesus transpacificus). Legacy and current-use pesticides, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) were quantified in a surrogate fish species (Wakasagi; Hypomesus nipponensis), sediments, zooplankton, and suspended solids throughout the Sacramento Deep Water Ship Channel (SDWSC). Forty-four of 63 analytes were detected across the tested media, with legacy pesticides (LPs), PAHs, and PCBs being the most prevalent contaminants measured in Wakasagi. Pyrethroids, a class of current-use insecticides, were rarely detected in Wakasagi tissue. Pattern analysis via cosine similarity showed that contaminant concentrations associated with suspended solids best reflected the concentrations measured within the Wakasagi, suggesting that suspended solids may represent a relevant exposure pathway. While only DDE and DDD concentrations exceeded the threshold effect concentration for sediment (TEC), contaminants associated with suspended solids exceeded most sediment quality guidelines. In addition, PAH concentrations in suspended solids exceeded multiple lesion thresholds for a variety of other fish species. These results suggest potential ecological concern from suspended solid-associated contaminant exposure. Future studies need to be performed to assess the relationship between HOCs associated with suspended solids and their potential harm to pelagic organisms for the purpose of contaminant mitigation in the SDWSC.
