Sweetwater Dam, Arch-gravity dam in San Diego County, United States

Sweetwater Dam is a concrete thick arch-gravity dam across the Sweetwater River, 108 feet (33 m) high and 700 feet (210 m) long, with a base 46 feet (14 m) thick. It impounds the 960-acre Sweetwater Reservoir, holding 28,079 acre-feet. An intake tower on the upstream side feeds a high-pressure conduit through the base, and two seven-gated spillways can pass more than 45,000 cubic feet per second.

The structure was completed in 1888 as a concrete construction and advanced water management technology in California. A major flood in 1916 caused damage that prompted engineers to redesign the spillway system.

The dam is listed as a Historic Civil Engineering Landmark. Its name comes from the Sweetwater River, and the reservoir is used today for recreation and wildlife management. The 1915 drought led San Diego to hire Charles Hatfield, the "rainmaker"; the rains that followed in January 1916 are still told as a local anecdote.

The dam itself is not open to visitors; the 960-acre Sweetwater Reservoir it impounds is the public face of the site, used for fishing and wildlife watching. Access is from the communities of Bonita to the southwest and La Presa to the northeast, roughly 12 miles east of San Diego. Expect only a trickle of water below the dam, since it holds back nearly all upstream inflow.

The main structure remained intact during the 1916 flood while its surrounding support systems failed. This experience changed how engineers designed spillway systems and influenced water control methods used elsewhere.