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 itself.