The Columbia River begins in southeastern British Columbia at Columbia Lake, located about 55 miles (93 kilometers) north of Cranbrook. Several major tributaries of the Columbia also originate in British Columbia, including the North Fork Flathead, Kootenai (spelled Kootenay in British Columbia), Kettle and Okanagon (spelled Okanagan in British Columbia). These, with the exception of the Kootenai, flow into the Columbia or other tributaries in the United States.

From the headwaters lake, the Columbia flows about 200 miles (321 kilometers) north then turns south and flows about 270 miles (434 kilometers) to the international border. British Columbia provides about 20 percent of the total water volume of the Columbia (although some of that water begins in the United States, such as the Pend Oreille/Clark Fork system, or flows from British Columbia into the United States and back into British Columbia, as with the Kootany/i River).

The Columbia in British Columbia historically was a salmon river. In 1807, explorer David Thompson, who discovered the river in Canada, observed salmon spawning in Columbia Lake and the next lake downriver, Windermere Lake. Lower in the Canadian course of the river, sockeye were known to spawn in the upper and lower Arrow Lakes between Castlegar and Revelstoke, a distance of about 100 miles (160 kilometers), and summer Chinook spawned in the area now flooded by Mica Dam. In 1879, members of the Palliser Expedition observed spawned-out salmon along the shore of the river from the mouth of the Braeberry River to the headwaters lakes, a distance of more than 150 miles. In October 1910, under the heading “Nelson News of the Day,” the Nelson [B.C.] Daily News reported:  “A beautiful salmon was landed at the pool, Slocan Junction, yesterday by Robert Elliott, weighing exactly 50 pounds. The fish was caught on rod and line, with a rather small spoon, and was landed after a fight of an hour and twenty minutes. Its length is four feet two inches. It will be on display this morning in the window of the Nelson Hardware company, with whose tackle it was caught.” The pool on the Kootenay was about a mile upstream from the point — Slocan Junction — where the Slocan River flows into the Kootenay River about half way between Nelson and Castlegar. The Slocan and Kootenay were salmon rivers, but salmon migration up the Kootenay at stopped at a series of waterfalls a short distance upstream from the Slocan Junction.

In the decades following the Depression the United States and Canada explored hydropower developments on the Columbia River and its major tributaries. Grand Coulee Dam was completed in 1941, ending salmon migration to the upper Columbia River. In the 1950s, hydropower planning accelerated, including public/private partnerships. In 1954 the government of British Columbia signed an agreement with the Kaiser Aluminum and Chemical Company to pursue construction of a $30 million dam on the Columbia River at Castlegar. However, the agreement stalled when the Canadian Parliament passed a law requiring a federal license. The following year, 1955, the Puget Sound Utilities Council proposed a $250 million dam at Mica Creek, site of the current Mica Dam, to produce 1,800 megawatts of power for the United States and 1,400 megawatts for Canada. Also in 1955 General Andrew McNaughton, chairman of the Canadian Section of the International Joint Commission, proposed diverting about two-thirds of the flow of the Columbia River at Revelstoke through the mountains to the Fraser River — where there were no dams — for power-production purposes. The Canadian Parliament appropriated funds to study the diversion, but it never was constructed.

In the late 1950s negotiations that had been ongoing between the United States and Canada regarding Columbia River hydropower developments culminated with agreement to build three dams in British Columbia — Mica, Keenleyside and Duncan — to store and release water for the purpose of maximizing hydropower generation at dams downstream in the United States. The agreement was codified in the Columbia River Treaty in 1962. The dams, completed in the late 1960s, served their purpose and provided the intended water storage and hydropower benefits, but they also took a toll on fish, wildlife, the economy, and culture of the Canadian Columbia Basin. Given the mountainous nature of the Columbia River Basin in Canada, there was little agricultural land as a percentage of the region, and by flooding the river valleys the reservoirs wiped out the most productive, and in some areas the only, agricultural land. Keenleyside Dam flooded town sites and farmland, as did the reservoir behind Libby Dam, which was built on the Kootenai River in Montana under authority of the treaty. Lake Koocanusa behind Libby Dam flooded river bottom land north across the international border into British Columbia. In all, more than 2,000 people were displaced by the construction of the Columbia River Treaty dams.

Little was done to compensate for these losses until 1995, when the province created the Columbia Basin Trust and provided a portion of the income from the additional hydropower sales for the Trust to spend on efforts to mitigate the social, economic, and environmental impacts of the dams. The 1995 Columbia Basin Trust Act established the Trust “... to help create a prosperous economy with a healthy and renewed natural environment.” The Trust is “... an autonomous and independent organization of communities,” according to its literature. Through the Trust, millions of dollars will flow into the Canadian Columbia River Basin from the sale of electricity in the United States — the “downstream benefits” — made possible by the operation of storage reservoirs behind the three Canadian dams of the 1962 Columbia River Treaty. The Trust manages a portfolio of investments that includes participation in tourism facilities and other economic development activities such as loans to small businesses.