The St. Mary River originates in the Rocky Mountains in northwestern Montana and flows north across the international boundary into Alberta, emptying into the Oldman River near Lethbridge. The St. Mary River has a fairly regular and dependable flow during the summer irrigation period because of its source in the high elevations of Glacier National Park. Winter flows are sustained by a ground-water base flow.

The North Milk and Milk Rivers originate in the foothills of the eastern slopes of the Rocky Mountains in Montana and flow northeasterly across the international boundary into Alberta. Downstream from the confluence of the North Milk and Milk Rivers, the Milk River flows eastward and roughly parallels the international boundary for about 120 river kilometres (70 miles) and then flows southeastward before it re-crosses the International Boundary into Montana and eventually empties into the Missouri River. The river flow is dependent on spring snowmelt and rainfall in the foothills and is thus less regular and dependable than the St. Mary River as a source of water.

The United States St. Mary Canal was constructed in 1917 and is used to divert water from the St. Mary River to the North Milk River for use in the lower Milk River valley in Montana.

The IJC provides direction for the measurement and apportionment of water that crosses the international boundary in the St. Mary and Milk River basins, in accordance with the Boundary Waters Treaty of 1909 and the IJC Order of 1921 (See Responsibilities of the Accredited Officers). Measurement of flow and determination of apportioned shares are conducted jointly by the Water Survey Division of Environment Canada and the U.S. Geological Survey (See Members). Measured and apportioned flows are documented in annual reports to the IJC (See Publications). Annual meetings of Environment Canada, U.S. Geological Survey, water managers, and other interested parties are held in February (See Publications for minutes). Some of the historical documents are also available in Publications.

Three of the eastern tributaries of the Milk River have sufficient current usage to also require a formal apportionment. These tributaries: Frenchman River, Battle Creek and Lodge Creek, begin in the Cypress Hills area of southeastern Alberta and southwestern Saskatchewan and flow in a southeasterly direction to join with the Milk River in Montana. Division of the water of these tributaries began in 1937 in the Frenchman River basin, 1957 in the Battle Creek basin and 1961 in the Lodge Creek basin. Reservoirs in the basins of these tributaries provide storage for irrigation in Alberta, Saskatchewan and Montana. The remaining major tributaries–Woodpile, East Fork Battle, Lyons, Whitewater, Rock, and McEachern Creeks–do not have sufficient usage in Canada to warrant a division of flow.

Responsibilities of the Accredited Officers

The responsibilities and duties of the Accredited Officers were outlined in the 1921 Order of the International Joint Commission respecting the St. Mary – Milk Rivers. The Accredited Officers (or “Reclamation and Irrigation Officers” as stated in the order) shall, until the 1921 Order is varied, modified, or withdrawn by the Commission, make jointly the measurement and apportionment of the water to be used by the United States and Canada according to the rules defined by the order. Specific duties outlined in Paragraphs V, VI, VII, and IX are as follows:

Paragraph V states:

“For the purpose of carrying out apportionment directed in Paragraphs I, II, and III hereof the said Reclamation and Irrigation Officers shall jointly take steps:”

  • To ascertain and keep a daily record of the natural flow of the St. Mary River at the international boundary, of the Milk River at the Eastern Crossing, and of the eastern tributaries of the Milk River at the international boundary by measurement in each case
    • At the gauging station at the international boundary;
    • At all places where any of the waters which would naturally flow across the international boundary at that particular point are diverted in either country prior to such crossing;
    • At all places where any of the waters which would naturally flow across the international boundary at that particular point are stored, or the natural flow thereof increased or decreased prior to such crossing;
  • To fix the amount of water to which each country is entitled in each case by applying the directions contained in paragraphs 1, 2, and 3 hereof to the total amount of the natural flow so ascertained in each case.
  • To communicate the amount so fixed to all parties interested, so that the apportionment of the said waters may be fully carried out by both countries in accordance with the said directions.

Paragraph VI states:

“Each country may receive its share of the said waters as so fixed at such point or points as it may desire. A gauging station shall be established and maintained by the Reclamation and Irrigation Officers of the country in which any diversion, storage, increase or decrease of the natural flow shall be made at every point where such diversion, storage, increase, or decrease takes place.”

Paragraph VIII directs the Accredited officers:

  • To make such additional measurements and to take such further and other steps as may be necessary or advisable in order to insure the apportionment of the said waters in accordance with the directions herein set forth.
  • To operate the irrigation works of either country in such a manner as to facilitate the use by the other country of its share of the said waters and subject hereto to secure to the two countries the greatest beneficial use thereof.
  • To report to the Commission the measurements made at all international and other gauging stations established pursuant to this order.

Paragraph IX states:

“In the event of any disagreement in respect to any matter or thing to be done under this order the said Reclamation and Irrigation Officers shall report to the Commission, setting forth fully the points of difference and the facts relating thereto.”