Boundary Dam is a concrete arch gravity-type hydroelectric dam on the Pend Oreille River, in the northeast corner of Washington State.
Boundary Dam rises 340 feet from its bedrock. The dam is 740 feet long at the top. It is 32 feet thick at its base and only eight feet thick at its crest.
Located adjacent to the dam, the powerhouse is completely built inside of the rock that makes up the left abutment of the dam.
Four turbines of approximately 208,000 horsepower each and two larger units of approximately 268,000 horsepower each produce 1040 MW at peak output, and can supply about 40 percent of Seattle's electricity demand.
The reservoir behind the dam is 17.5 miles long, extending through mountain forests and the towns of Metaline Falls and Metaline to the base of the Pend Oreille PUD's Box Canyon Dam.
Boundary's output is wheeled throughout the western United States via the Bonneville Power Administration transmission lines