Lower Granite Lock and Dam is a concrete gravity run-of-the-river hydroelectric dam on the Snake River, and bridges Whitman County and Garfield County, in the U.S. state of Washington.[4] The dam is located 22 miles (35 km) south of the town of Colfax, and 35 miles (56 km) north of Pomeroy.

Lower Granite Lock and Dam is part of the Columbia River Basin system of dams. It was built and is operated by the United States Army Corps of Engineers. Power generated is distributed by the Bonneville Power Administration.

Lower Granite Lake, which extends 39-miles east to Lewiston, Idaho, is formed behind the dam. Lake Bryan, formed from Little Goose Dam, runs 37 miles (60 km) downstream from the base of the dam.

Construction of Lower Granite Lock and Dambegan in July 1965. The main structure and three generators were completed in 1972, with an additional three generators finished in 1979. Generating capacity is 810 megawatts, with an overload capacity of 932 MW. The spillway has eight gates and is 512 feet (156 m) long. An 86 x 674 ft. navigation lock was also included in construction.

Lower Granite Dam is the most upstream dam in the Snake River system that has fish ladders (2) to allow adult salmon and steelhead to migrate upstream. The Columbia River treaty tribes along with some environmental groups have recommended that this dam along with the other three lower Snake River dams be decommissioned and/or removed because of their impact on endangered salmon and steelhead populations. A significant increase in the Sockeye Salmon return to the Columbia River in 2008 proved a pleasant surprise and raised hopes for increased salmon runs across the Lower Granite. Wildlife officials were not certain of the reason for the increased salmon return (Idaho Statesman, June 28, 2008) The Army Corps of Engineers has installed new devices such as removable spillway weirs in an attempt to make the dam less harmful to juvenile salmon.

There is also a juvenile bypass/collection facility that collects juvenile migrating salmon and steelhead so they can be transported downstream by barge.

Lower Granite Dam
Locale Garfield / Whitman counties, Washington, USA
Construction began July 1965
Opening date 1984
Construction cost $624,098,663
Dam and spillways
Type of dam Concrete-gravity, run-of-the-river
Height 100 feet (30 m)
Length 3,200 feet (980 m)
Impounds Snake River
Type of spillway Service, gate-controlled
Spillway capacity 850,000 cubic feet per second (24,000 m3/s)
Creates Lower Granite Lake
Capacity 710,189,333 cubic yards (542,978,705 m3)
Surface area 8,900 acres (36 km2)
Power station
Type Yes
Turbines 6 x 135-155 MW units
Installed capacity 810 MW
Maximum capacity 932 MW