Lake Oahe Lake Oahe Lake Oahe (oh-WAH'-hee) is a large reservoir behind Oahe Dam on the Missouri River; it begins in central South Dakota and continues north into North Dakota in the United States. The lake has an area of and a maximum depth of . By volume, it is the fourth-largest reservoir in the US. Lake Oahe has a length of approximately and has a shoreline of . 51 recreation areas are located along Lake Oahe, and 1.5 million people visit the reservoir every year. The lake is named for the 1874 Oahe Indian Mission. Lake Oahe begins just north of
Boundary Dam Boundary Dam Boundary Dam is a concrete arch gravity-type hydroelectric dam on the Pend Oreille River, in the U.S. state of Washington. The dam is located in the northeast corner of Washington state, just south of the border with British Columbia, Canada. It is operated by Seattle City Light and makes up a significant portion of the City of Seattle's energy portfolio. On average, it provides upwards of 46% of the power generated by Seattle City Light. Boundary Powerhouse, located adjacent to the dam, is completely built inside of the rock that makes up the left abutment of the dam