Lake Koocanusa is a transboundary reservoir located in southeastern British Columbia and northwestern Montana. The reservoir was officially impounded in 1972 after construction of Libby Dam, which began in 1966. The dam was constructed as part of a treaty between the United States and Canada to cooperatively develop the water resources of the Columbia River drainage basin. The reservoir has a volume of 7.16 km3 and provides flood storage, hydroelectric power production, and recreation benefits. The 148-km reservoir straddles the United States-Canadian border and impounds water from about 23,271 km2 , or 47 percent, of the Kootenai River drainage basin. Historic and present-day mining of metallurgical coal in the Canadian headwaters have significantly degraded water quality within the rivers that drain to Lake Koocanusa within the United States, posing serious threats to river health and human safety.