El Capitan Reservoir, reservoir in San Diego County, California, United States

El Capitan Reservoir lies in the Cuyamaca Mountains about 30 miles northeast of San Diego, two miles northwest of Alpine. Its 237-foot dam on the San Diego River is built of hydraulic fill, not concrete, and holds 112,800 acre-feet for San Diego's drinking water. The reservoir is owned by the city of San Diego.

The 237-foot dam, built of hydraulic fill, was completed in 1934 to supply San Diego with drinking water. To clear the site, the Kumeyaay people were forcibly relocated to the Capitan Grande Reservation. After the 1971 San Fernando earthquake, state engineers restricted the reservoir's maximum water surface to 30 feet below the spillway.

The reservoir flooded the Kumeyaay village of Capitan Grande; its residents were forcibly relocated to the Capitan Grande Reservation to clear the site. The reservoir and dam take their name from that displaced community, and the reservation remains nearby today.

Boating is limited to canoes, kayaks and row boats; personal watercraft, standup paddle boarding and water skiing are not permitted. Fishing is allowed all year, but the reservoir is closed on Wednesdays, Thursdays and the first Friday of each month. There is no camping at the lake; the nearest sites are 8.5 miles away at Lake Jennings and 12.5 miles away at Viejas Campground.

The reservoir's water usually comes from runoff above the dam, but in drought years it is sometimes piped in from San Vicente Reservoir, the terminus of the First San Diego Aqueduct. Annual inflow has ranged from 1,000 to 70,000 acre-feet over a 25-year period.