Libby Dam is 422 feet tall and 3,055 feet long. Lake Koocanusa is 90 miles long with a maximum depth of about 370 feet. Forty-two miles of Lake Koocanusa are in British Columbia, Canada.

The Kootenai River is the third largest tributary to the Columbia River, contributing almost 20 percent of the total water in the lower Columbia. Only the Snake and Pend Oreille/Clark Fork Rivers contribute more.

Libby Dam holds back 5.8 million acre-feet of water. An acre-foot of water is one acre of land covered with one foot of water, equaling 325,804 gallons. Spread out one foot deep, the lake would cover an area larger than the state of Massachusetts!

Surprisingly, Koocanusa is not an Indian name. Mrs. Alice Beers from Rexford, Montana, won a contest in 1971 to name the Libby Dam reservoir. She combined the first three letters from KOOtenai River, the first three letters of CANada, and USA.

Libby Dam is a “straight-axis, concrete gravity” structure solidly anchored in bedrock. “Straight-axis” means the dam is built straight across the river instead of curved or arched. “Concrete gravity” means Libby Dam is made of concrete and holds back the water of the Kootenai River with its own massive weight. The 7.6 million tons of concrete in Libby Dam is enough to build a two-lane highway from Libby, Montana, to Washington, D.C. (2,290 miles).

Libby Dam was built to provide flood protection for the Kootenai and lower Columbia Rivers, as well as to provide an additional source of hydroelectric power to meet increasing energy demands. Water stored behind Libby Dam also provides increased stream flows to downriver dams and powerhouses when water levels are low during winter months and in times of drought.

The Kootenai River flowed wildly before Libby Dam was built, causing floods in Montana, Idaho and British Columbia.

Historically, May and June were months of sandbags and anxiety! A total of $522 million in flood damages were caused by the Kootenai River from 1948 through 1961.

The Dam was built here because a large amount of water could effectively be stored. Any other site in the area would have required a longer, more costly structure and may have flooded more land.

At the peak of construction, the project employed over 2,000 workers. To offset this burden on the local communities, the Corps built three new schools, additions to several other schools, and the Libby airport. The Corps moved the town of Rexford to higher ground and built a new school, a water system, a sewage system, a fire station, a post office and roads. State highway 37 was also relocated. A forest development road was established along the west side of the reservoir. Koocanusa Bridge, Montana’s longest (2,437 feet) and highest (270 feet), was built to provide access across the reservoir. Relocating the Great Northern Railroad line was one of the most complex of all the projects. Relocation cost more than $100.6 million - nearly 20 percent of the total dam construction budget-and included a seven-mile railroad tunnel through Elk Mountain.

Congress authorized construction of Libby Dam in 1951. The Columbia River Treaty between Canada and the United States was signed in 1961 and ratified in 1964. This treaty provided for construction of three storage dams in the Canadian portion of the Columbia River Basin (Duncan, Mica, and Hugh Keenleyside) and permitted the United States to construct Libby Dam. The four dams provide 25.5 million acre-feet of water storage to be used by both countries.

Construction began in 1966. It took the U.S. Army Corps of Engineers and its prime contractor, Morrison Knudsen Construction Company, until 1972 to complete Libby Dam. President Ford and Minister of Energy McDonald dedicated the facilities and ceremonially put the first power on line in August 1975. The powerhouse, was completed in 1976.

Reprint of Corps of Engineers pamphlet.