Lake Entiat, reservoir in Chelan and Douglas counties, Washington, United States

Lake Entiat is a large reservoir on the Columbia River between Chelan and Douglas counties in Washington state. The water stretches across a wide area and is held back by a dam that was built to manage water flow and produce electricity.

Rocky Reach Dam, completed in 1962 on the Columbia River, impounds Lake Entiat, also called Rocky Reach Reservoir. The reservoir flooded the south bank where Turtle Rock stood, turning that rocky outcrop into a 150-acre island; the old route of U.S. Highway 2 crossed the land it now occupies. In the 1800s Chinook people lived at the confluence of the Columbia and Entiat rivers, a spot they called Enteatqua, meaning "fast water" or "rapids", the name later given to the river and the town of Entiat.

The area is easily accessible from several roads, with parking areas and boat launch sites nearby. Visitors will find picnic spots, restrooms, and basic facilities at surrounding parks, especially during the warmer months.

Turtle Rock Island, a 150-acre rocky outcrop northeast of Lincoln Rock State Park, was once part of the mainland on the Columbia's south bank. It became an island when the reservoir filled, and U.S. Highway 2 once ran through the ground it now covers; road remnants can still be seen in aerial photos. The island is a nature preserve and fish hatchery, reachable only by boat.