Bay-Delta Plan Threatens 12% Water Supply Cut as Golden Mussels Spread Across District

The Contra Costa Water District Board of Directors faced a pair of sobering briefings April 15 — one on an invasive species now confirmed at virtually every intake, the other on a state regulatory plan that could slash water deliveries in the years the district needs them most. Together, the two threats signal a new era of rising costs and operational complexity for the East Bay water provider.

• Bay-Delta Plan nearing October 2026 adoption could reduce water supply by 12% in critically dry years — and up to 34% under a stricter flow threshold
• Golden mussels detected at all CCWD intakes and Los Vaqueros Reservoir, with $925,000 in response costs this fiscal year alone
• Staff identifies likely errors in the state's environmental analysis that underestimate impacts on the district
• District doubles employee participation in educational programs, builds new internship pipeline with City of Antioch and Mt. Diablo Unified School District
• Canal pool cleaning complete; Rock Slough diversions and Los Vaqueros filling resume, adding roughly 5,000 acre-feet of stored supply

The basics: The State Water Resources Control Board released a revised draft Bay-Delta Plan in December 2025 that would reset how much water can be drawn from the Sacramento-San Joaquin Delta — the source that supplies CCWD and much of the state. The plan offers two implementation pathways: a voluntary agreements track called Healthy Rivers and Landscapes, and a regulatory track requiring 55% of unimpaired flow year-round (adjustable to 35% for water supply). The State Board is targeting adoption by October 2026, with implementation taking two or more years beyond that.