Improving Water Reliability While Enhancing Fish Habitat on the Calaveras River

The Bellota Weir Modification is a major infrastructure and habitat restoration effort led by the Stockton East Water District (SEWD) on the Calaveras River near Mormon Slough in San Joaquin County, California. The effort is being undertaken to comply with requirements in SEWD’s Calaveras River Habitat Conservation Plan (HCP), approved by the National Marine Fisheries Service in 2020, which mandates upgrades to aging diversion facilities to improve fish passage and protect environmental site assessment-listed species such as Central Valley steelhead and Chinook salmon.

HDR has been leading a multidisciplinary team to design a new fish passage. Under HCP and related permitting, the project replaces the existing flashboard dam, temporary fish ladder and cement sill with modern infrastructure designed to balance water delivery reliability and ecosystem needs. Key components include a new screened diversion intake with multiple cylindrical fish screens, an inflatable Obermeyer weir, roughened channels and nature-like rock slope fishways, a fish-exclusion structure to prevent entrainment into dead-end channels, and improved conveyance pipelines and access facilities. These features are intended to keep salmonids on suitable outmigration routes, enhance volitional passage upstream and downstream, and reduce fish entrainment while providing more dependable supplies to SEWD’s agricultural and municipal users.

The project also supports broader water management goals, including groundwater recharge and water quality improvements, and has secured significant funding and contracts to advance construction, which began moving forward in 2025. Through these upgrades, SEWD aims to modernize aging infrastructure to improve water-delivery reliability for Stockton East Water District’s customers, meet federal and state conservation obligations, and enhance long-term habitat conditions for threatened fish species.