Rimrock Lake is a lake along the course of the Tieton River, in Yakima County, Washington state, US.

Rimrock Lake
Aerial view of Tieton Dam and Rimrock Lake from the downstream side of the dam.
Rimrock Lake
Location	Yakima County, Washington, United States
Coordinates	46°39′23″N 121°07′46″W / 46.65639°N 121.12944°W / 46.65639; -121.12944
Type	reservoir
Primary inflows	Tieton River
Primary outflows	Tieton River
Catchment area	187 sq mi (480 km2)
Basin countries	United States
Max. length	6 mi (9.7 km)
Max. width	1 mi (1.6 km)
Water volume	0.0586 cu mi (0.244 km3)
Surface elevation	2,926 ft (892 m)

The lake is used as a storage reservoir for the Yakima Project, an irrigation project run by the United States Bureau of Reclamation. An impoundment of the Tieton River, Rimrock Lake's capacity and discharge is controlled by Tieton Dam, a 319-foot (97 m) high structure built in 1925. Rimrock Lake's active capacity is 198,000 acre⋅ft (244 million m³).^[1]

Upstream from the lake, the Tieton River is impounded by Clear Creek Dam, another element of the Yakima Project. About 8 miles (13 km) downstream from Rimrock Lake the Tieton River is tapped by the Tieton Diversion Dam, supplying water to the Tieton Main Canal. The canal supplies irrigation water to the Tieton Division of the Yakima Project, with excess and agricultural runoff draining into Ahtanum Creek, west of Yakima.^[1]

Near the lakes are the communities of Rimrock and Silver Beach. The lake flooded the site of a Yakama village named Miya’wax and portions of the Yakama-Cowlitz Trail which connected the Yakama people east of the Cascade Range to the Cowlitz people west of the mountains.^[2]