From the late 1800s, when the first hydropower turbines were installed on Columbia River tributaries, into the 1960s water power from dams in the Columbia River Basin provided most of the electricity in the Pacific Northwest. Then, as population increased and the regional economy grew, demand for electricity surpassed the output of the dams.
Other types of power plants were built, steadily adding to the region’s electricity supply. Primarily these were baseload coal and nuclear steam-electric plants and small peaking combustion turbines fueled by natural gas. Later, the system was further expanded by the addition of highly efficient natural gas combined-cycle plants. Beginning in the early 2000s, large numbers of wind turbine generators were added to the system.
Electricity in the Northwest still is dominated by hydropower, which accounts for about 54 percent of the supply capacity. The amount of hydropower varies with water conditions. Most of the region’s hydropower is generated on the Columbia River and its tributaries, but there also are dams on other rivers, particularly those that empty into Puget Sound. In years when precipitation and runoff are normal, the region’s hydroelectric system can provide about 16,000 average megawatts of electricity (an average megawatt is one million watts supplied continuously for a period of one year). The amount can be as much as 20,000 in a wet year or as little as 12,000 in a dry year. The page also has inc=formation abu carbon emissions from power production and additions and retirements of generating capacity.
As of March 2021, about 8.1 percent of the region’s electricity capacity comes from plants that burn coal, with plants that burn natural gas providing 15.2 percent (11.8 percent baseload and 3.4 percent peaking). The region’s single operating nuclear plant, located in eastern Washington, accounts for 1.9 percent of the region’s capacity. In all, the region’s power supply capacity totals about 64,340 megawatts. Here is a link to the Council's Power Supply page, which includes pie charts of regional capacity and average annual energy ("generating capability"), arranged by percentage of contribution from each type of generation.