The proposed expansion of Pacheco Reservoir in southern Santa Clara County is not solely a project aimed at improving our region’s ability to store water for droughts and emergencies.
A collaboration between Valley Water, the San Benito County Water District and Pacheco Pass Water District, the proposed expansion will improve the quality of fish habitat downstream of the dam.
Currently, Pacheco Reservoir is not large enough to allow for sufficient releases of water into Pacheco Creek to support the South-Central California Coast Steelhead, a fish population listed as federally threatened.
The South-California Central Coast Steelhead migrate and spawn in watersheds that flow into Monterey Bay and the Pacific Ocean, such as the Pajaro, Salinas, Carmel and Big Sur rivers. The juvenile fish are reared (grow and develop) in freshwater streams before migrating to the ocean to grow and mature, and then return as adults to reproduce in the same freshwater systems where they hatched.
The proposed expansion will increase the reservoir’s capacity from 5,500 acre-feet to up to 140,000 acre-feet. By increasing the reservoir’s capacity, Valley Water and its partners will have the ability to store more of the native water, which can then be used to further enhance habitat for the threatened steelhead.
The larger reservoir will provide water storage and emergency water supply benefits to Santa Clara and San Benito counties. A bigger and deeper reservoir will also create a reserve of more water and cooler water to release into Pacheco Creek throughout the year, providing suitable flow and water temperatures to support the migration and survival of the South-Central California Coast Steelhead.
A more robust year-round water flow in Pacheco Creek will improve approximately 10 miles of habitat that could support threatened steelhead. The resulting delivery of more consistent flows of cooler water is expected to provide migration opportunities, elevate the survival of steelhead eggs and fry, and provide adequate conditions for summer rearing in Pacheco Creek, improving the long-term survival of this cold-water fish.