St. Mary / Milk River - 1909 Boundary Waters Treaty

The Development of Irrigation in Southern Alberta

Construction of Milk River Canal
Construction of Milk River Canal, 1904
Glenbow Archives PD-310-21

    In the late 19th Century irrigation was seen as crucial to promoting growth and creating prosperity in southern Alberta.

In 1894, the Canadian Parliament passed the Northwest Irrigation Act, which vested the right to the use of all water for any purpose in the Crown.

In 1896, the first surveys were carried out to examine the possibility of diverting water from the St. Mary River to the Lethbridge plains. Development soon began on diversion canals and other irrigation works to supply water to southern Alberta.

Several successful irrigation projects resulted in increased settlement of the area, creating towns such as McGrath and Raymond.


Irrigating alfalfa
Irrigating alfalfa, 1904
Glenbow Archives PD-863-15

Success Creates Greater Demand

Continuing growth in southern Alberta created the need for more water. During the same period growth in the State of Montana was also placing water demands on the St. Mary and Milk Rivers.

Map of  the St. Mary and Milk River
Click to enlarge

The Milk River originates in the Montana Foothills and flows north east into Alberta. Once in Alberta, the Milk river travels parallel to the Montana border for about 150 kilometres before turning south east and crossing back into Montana.  The St. Mary River originates in the high mountain areas of Many Glacier Park in Montana and flows north into Alberta. The St. Mary continues north for 100 kilometres emptying into the Oldman River and becoming part of the Saskatchewan River system.

As the St. Mary and Milk Rivers both originate in western Montana and flow north into Alberta, the origin and path of the flow means that water negotiations concerning the two rivers are international. When the Boundary Waters Treaty (1909) between Canada and the United States was signed, the division of the flow of the St. Mary and Milk Rivers between Canada and the United States was specified in Section VI.

The Treaty also established the International Joint Commission (IJC) composed of three members from Canada, and three from the United States, to examine and report on any issues referred to it by the member nations.

1917 Diversion of the St. Mary River

In 1917 the United States constructed a canal to divert water from the St. Mary River in western Montana to the Milk River. The diverted water flows in the Milk River channel into Alberta and is conveyed across southern Alberta for irrigation in eastern Montana.

Water diversion canal Water diversion canal

1921 Order of the International Joint Commission (IJC)

Canada and the United States could not agree on how the Treaty of 1909 should be interpreted nor could they agree on how water was to be measured or apportioned with regard to the St. Mary and Milk Rivers. The Canadian position was that the prior apportionment specified in the Treaty should be subtracted from the total flow of the two rivers prior to their equal sharing and river flow to be shared should be based on the flow at the mouth of the two rivers.

In 1921, after six years of hearings in Canada and the United States, and a legal reconstruction of intent, the IJC issued an order with rules clarifying how measurement and apportionment would take place.

  • Prior appropriations could be excluded from being shared equally.
  • The flow to be shared is the flow at the final border crossing of each river.
Rocky landscape    

St. Mary River and Milk River: Ongoing issues

In 2003, Montana wrote to the IJC stating the 1921 Order was not fair and requesting it be opened for review. In 2004, the IJC held public hearings to determine if the 1921 Order should be reviewed regarding the interpretation of how the water from the two rivers is shared.

In 2005, the IJC established a Joint Task Force of technical staff from Canada and the United States, as well as specifically from Alberta, and Montana, to review Administrative Measures. These Measures are the actual calculation methods used to determine each countries’ share of water based on the entitlement defined in the 1921 Order.

Because the Joint Task Force was unable to reach consensus, they recommended that Alberta and Montana work together at a watershed level to address the issue. The IJC then approached the governments of Alberta and Montana with the request they work together to address how each country could get better access to their respective entitlements.

Montana – Alberta St. Mary and Milk Rivers Water Management Initiative

The purpose of the Initiative is to explore and evaluate options for improving Alberta’s and Montana’s access to their respective share of the water of the St. Mary and Milk Rivers and make a joint recommendation on preferred options to provincial and state governments for their consideration and approval. The Premier of Alberta and the Governor of Montana approved the Terms of Reference for the initiative. A joint initiative team was appointed to explore options and make recommendations to the premier and governor.

    Water running under a bridge

Goal: Montana and Alberta develop an adaptive, dynamic, joint water management decision-making process that provides secure supplies for people and the environment.


Page Information

Updated: Dec 15, 2015