There are 46 developed waterpower projects having a total installed generating capacity of 1,472 megawatts (1 MW equals 1,000 kilowatts) in Idaho or on the State boundary line. When sites affecting two or more States are divided equally with the adjoining State, Idaho's allotment is 44 plants with an installed capacity of 1,025 megawatts. The gross theoretical capacity of the developed sites is 1,396 megawatts and of the undeveloped sites is 9,279 megawatts or a total of 10,675 megawatts. Power was computed for gross head, 100 percent efficiency, and average discharge. Grouped by magnitude of capability, there are 781 megawatts at 122 sites with individual capabilities of 1 to 4.99 megawatts, 2,744 megawatts at 120 sites with capabilities between 5 and 19.99 megawatts, and 7,150 megawatts at 63 sites with capabilities greater than 20 megawatts.

The Snake River and its tributaries drain about 87 percent of Idaho's total area and contain 94 percent of its potential waterpower. The greatest areal concentration of waterpower, except for isolated reaches of the Snake River, is in the Clearwater River basin with about 264 kilowatts of theoretical potential per square mile. The gross theoretical power of the Salmon River basin, 3,326 MW, is the greatest of all Idaho rivers including the main stem of the Snake River.

The first hydroelectric plant in Idaho was placed in operation in 1881. Waterpower has played an important part in the economy of Idaho since that time, and the State is in ninth place nationally in installed capacity of waterpower plants. Privately-owned plants produce 87.5 percent of the present average annual hydroelectric energy, and publicly-owned plants produce 12.5 percent. The principal producers are Idaho Power Company, Washington Water Power Company, Utah Power and Light Company, the Bureau of Reclamation, and the Corps of Army Engineers. The waterpower resources of Idaho are being actively developed at the present time and indications are that this active development rate will continue or accelerate.