Answer:
Hydroelectric
Step-by-step explanation:
Hydropower is the largest source of electricity in the Pacific Northwest, accounting for about 51% of the supply. The Columbia River provides the Pacific Northwest with the largest source of hydropower on the continent. The river's 31 hydroelectric dams can produce 22 GW of power.
In Oregon, hydroelectric power is the largest portion of the state's electricity resource mix, followed by coal and natural gas. In Washington, roughly two-thirds of the state's electricity comes from hydropower, but a quarter still comes from fossil fuels, namely coal and natural gas.