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Lake Oahe
A 231-mile Missouri River reservoir across the Dakotas
Lake Oahe turns 231 miles (372 km) of the Missouri River into a single winding reservoir, from just above Pierre, South Dakota, almost to Bismarck, North Dakota. With about 23.5 million acre-feet (29 km³) of capacity and roughly 2,250 miles (3,620 km) of shoreline, it ranks among the largest reservoirs in the country. The Army Corps of Engineers began Oahe Dam in 1948 as part of the Pick-Sloan Plan for flood control, irrigation and power, and President John F. Kennedy dedicated the rolled-earth dam on August 17, 1962. It stands 245 feet (75 m) high and 9,360 feet (2,850 m) long.
The lake's benefits came at a cost borne mostly by Lakota people. Its waters covered tens of thousands of acres of Missouri River bottomland on the Standing Rock and Cheyenne River Sioux reservations, the timbered river valleys where families lived, gathered and hunted, and forced entire communities to relocate to the uplands. Today the reservoir draws anglers for walleye and stocked Chinook salmon, and its water supplies tribal and rural communities along its banks. The dam's turbines, with an installed capacity of about 786 megawatts, feed power into the federal grid across the northern plains.
Since 2017 the Dakota Access Pipeline has carried crude oil under Lake Oahe about half a mile upstream of the Standing Rock Sioux Reservation, a crossing the tribe opposed over risks to its drinking water and treaty rights. The dispute drew thousands of protesters in 2016 and 2017. Federal courts later ordered a full environmental review, and the Corps released it in December 2025. In May 2026 the Corps signed a decision granting the easement with added leak-detection and monitoring conditions.