Calero Reservoir, Reservoir in the Almaden Valley, San Jose, California, US

Calero Reservoir is a man-made lake in Santa Clara County, California, formed by an earthen dam that captures runoff from the surrounding mountains and canyons. The lake sits within a county park that includes trails for hiking, equestrian use, and picnic areas along the shoreline.

The reservoir was created in 1935 following a voter-approved water plan from 1933, drawn up to secure reliable water sources during the Great Depression. The dam was built to collect runoff from the hills and supply the growing communities of the Santa Clara Valley.

The park around the reservoir is used by hikers, equestrians, and families who come regularly to enjoy the trails along the water's edge. Boating is permitted on the lake, which gives the area a relaxed, outdoor character on weekends.

The park around the reservoir is open for hiking, horseback riding, and picnicking, but swimming is not allowed to protect water quality. Anyone planning to bring a boat should check the current rules in advance, as not all watercraft are permitted.

A 2012 engineering study found alluvium beneath Calero Dam that could liquefy in an earthquake, so the reservoir is held 19 feet below the spillway, limited to about 45% of capacity or 4,414 acre-feet. Retrofit work may only start after Anderson Reservoir's retrofit finishes in 2031, when capacity could return to 9,738 acre-feet.