Briones Reservoir, located in western Contra Costa County, California, is the largest of East Bay Municipal Utility District's (EBMUD) five East Bay terminal reservoirs. With a capacity of 60,510 acre-feet and a watershed of 8.59 square miles, this open-cut water storage reservoir is primarily used for drinking water.

Paddling is strictly prohibited on Briones Reservoir due to its status as a potable water source. EBMUD enforces strict regulations to protect water quality, prohibiting fishing, swimming, wading, and any form of water contact. The only watercraft permitted are those used by select college rowing teams from Mills College, UC Berkeley, and Saint Mary's College, who must follow specific rules including boat inspections to prevent contamination.

While paddling is not allowed, the reservoir offers scenic views for hikers. Two trails, the Bear Creek Trail and the Oursan Trail, form a 14-mile loop around the reservoir. The trailhead is located at the Bear Creek Staging Area within Briones Regional Park. Hikers must obtain a Trail Use Permit from EBMUD for $10. Horseback riding is permitted, but mountain biking is not allowed on these trails. Dogs are only allowed on the Oursan Trail segment and must be leashed.

The reservoir is surrounded by rolling hills and provides habitat for various wildlife. Visitors may observe animals such as deer, coyotes, and various bird species from the surrounding trails. The Briones Dam, an earthen dam completed in 1964, impounds the reservoir.

For those interested in the area's history, the reservoir partially submerges the valley where Bear Creek once flowed. The creek still enters the reservoir from the eastern section, contributing to its water supply along with imported water from the Mokelumne River via the Briones Aqueduct.