Protecting pallid bats during Anderson Dam construction

September 11, 2026

To help minimize the potential impacts of construction at Anderson Dam, Valley Water built an alternative roost that provides the colony with an additional safe place to shelter.

As part of the Anderson Dam Seismic Retrofit Project, Valley Water has built an alternative bat roost to help protect one of Santa Clara County's most important pallid bat colonies.

California named the pallid bat as its official state bat in 2024, recognizing the important role bats play in the state’s ecosystems and agricultural economy. Pallid bats provide natural pest control by feeding on insects and other arthropods. They are also recognized as a California Species of Special Concern, highlighting the importance of protecting their established colonies and habitat.

Less than a half mile from Anderson Dam, a barn on Cochrane Road serves as the primary roost for the largest and most stable known pallid bat maternity colony in Santa Clara County, supporting up to 100 bats each year. Female pallid bats gather there to give birth and raise their pups until the young bats can fly and forage on their own.

Construction noise and vibration from the Anderson Dam Seismic Retrofit Project could disturb the bats at their primary roost. To help minimize potential impacts, Valley Water built an alternative roost that provides the colony with another safe place to shelter if construction activity affects conditions at the Cochrane Road barn.

The new bat roost is located approximately 1.5 miles from Anderson Dam. Wildlife biologists developed a custom roost to meet the unique needs of pallid bats. The 12-by-12-foot structure stands about one and a half stories tall, elevating the bats above the ground to help protect them from predators.

The bat house features four narrow, three-quarter-inch entrance slots that allow bats to climb inside. Its open interior provides space for the colony to gather before leaving at dusk to forage for prey. Foam insulation and a water jacket built into the walls and roof help regulate temperatures year-round, creating a stable environment that closely resembles the bats' preferred roosting conditions.

By providing an alternative roost and minimizing disturbance during construction, Valley Water is helping protect this important colony while advancing critical seismic safety improvements at Anderson Dam. The effort demonstrates how environmental stewardship and public safety can go hand in hand.

A water jacket installed inside the bat roost helps regulate temperatures and create stable roosting conditions for pallid bats.

Wood framing takes shape inside the custom-designed pallid bat roost near Anderson Dam.

Valley Water manages an integrated water resources system that includes the supply of clean, safe water, flood protection and stewardship of streams on behalf of Santa Clara County's 2 million residents. Valley Water effectively manages 10 dams and surface water reservoirs, three water treatment plants, an advanced recycled water purification center, a state-of-the-art water quality laboratory, nearly 280 acres of groundwater recharge ponds and 350 miles of waterways. We provide wholesale water and groundwater management services to local municipalities and private water retailers who deliver drinking water directly to homes and businesses in Santa Clara County.