January 11, 1909, is the official date of the International Waterways Treaty, also known as the Boundary Waters Treaty. The treaty between the United States and Great Britain addresses boundary water issues that might arise between the United States and Canada, such as on the Columbia’s transboundary tributaries and the river itself. The Treaty established the International Joint Commission to act as a tribunal to investigate such matters.

Professor Nigel Bankes of the University of Calgary law school, who has written extensively on the treaty, says the countries intended it to address three objectives. First, the treaty stipulated certain provisions of international river law; second, the treaty established the International Joint Commission and gave it jurisdiction over water projects that would change the levels of boundary waters or would result in flooding in the other country; third, the treaty addressed two specific disputes — the Niagara River and the level of Lake Erie; and the levels of the St. Marys and Milk rivers in central and eastern Montana.

Neither the Columbia River nor its tributaries are “boundary waters” as defined by the treaty, which are waters that actually form the boundary between the two countries. However, the treaty, in Article IV, provides that neither country may change the level of transboundary waters at the boundary without the approval of the International Joint Commission. This provision would be invoked by the Commission in its 1941 approval of the construction of Grand Coulee Dam. Ironically, perhaps, the dam already had been built when the Commission took up the matter, but the issue was whether the river level at the border — specifically at the town of Trail, B.C., about a mile above the border — would be affected by the reservoir created by the dam.

Article II of the treaty reserves to the United States and Canada the exclusive jurisdiction and control over waters “which in their natural channel would flow across the boundary,” according to Professor Bankes. In short, this means that an upstream country can divert or use a river as it sees fit without concern for the impacts downstream in the other country (this is consistent with the Harmon Doctrine, which grew out of a dispute with Mexico over Colorado River water at about the same time as the Boundary Waters Treaty). But other countries have rejected that premise in favor of sharing international rivers and agreeing not to cause harm to the downstream country.  From time to time, Canada has proposed diverting the Kootenay River into the Columbia at the headwaters, Columbia Lake, which would have consequences downstream on the Kootenai in Montana and Idaho and also on the mainstem Columbia.

Article II includes a limited cause of legal action if river operations in the upstream country injure private parties in the downstream country. Article II has been cited in establishing operations of dams on transboundary tributaries of the Columbia, such as the Kootenai and Pend Oreille.