International Hydrological Studies of Wyoming-Montana Water Science Center

Science Center Objects

The USGS serves as the lead agency for the United States to measure and apportion natural flows of the St. Mary and Milk Rivers according to the Boundary Waters Treaty of 1909 and the International Joint Commission Order of 1921. The division of water between the United States and Canada is overseen by the Accredited Officers of the St. Mary and Milk Rivers, who are appointed by their respective governments.

Chief Mountain

Chief Mountain

(Public domain.)

The United States’ share of water is primarily used by the U.S Bureau of Reclamation - Milk River Project, which diverts St. Mary River water into the Milk River watershed.

The project, locally known as “the lifeline to the highline,” meets the needs of residents and industry along the Northern Tier of Montana to:

  • Irrigate approximately 121,000 acres;
  • Supply water to municipalities and domestic users; and
  • Fulfill Tribal water rights.

Project Objectives

  • Measure and report hydrologic data from the St. Mary and Milk Rivers flowing within the United States.
  • Collaborate with Water Survey Canada and Provincial Government officials to apportion water according the 1909 Treaty and International Joint Commission Order of 1921.
  • Address technical challenges and modernize apportionment methodology and techniques.
International Hydrological Studies Map

International Hydrological Studies Map

(Public domain.)


Annual Report to The International Joint Commission on The Division of Waters of the St. Mary and Milk Rivers


Important links

International Joint Commission

Current Streamflow Conditions in Montana

Water Survey Canada