In fact, according to the Grand Coulee Webpage, the Grand Coulee dam is the largest producer of hydro-electric power in the United States and is the third largest producer in the world. The Grand Coulee is located on the Columbia River in central Washington. According to the BPA, it can generate up to 6,809 MW of power. In the Pacific Northwest, the Chief Joseph dam is the second largest producer, generating up to 2,614 MW of power, and the John Day dam comes in third at 2,480 MW of power.