Milk River Project

St Mary and Milk River Project Story Map

Click the link above to view an interactive and user friendly story map of the St Mary Diversion and Milk River Project.


The Milk River Project is an irrigation project authorized in 1903 intended to supply the Lower Milk River valley with water for irrigation. The St. Mary’s diversion dams, canals, drops, and siphon were completed in in 1917 and still remain in-use today. Additional construction and another steel siphon was later added due to the high demand for water. The St. Mary’s conveyance system was designed as a single-purpose system for irrigation.  However, multiple towns, businesses, recreation, and wildlife benefit from the Milk River. One of the goals of the MRWA is to educate the Milk River Basin residents on the importance and critical need for the rehabilitation of the 100 year old diversion infrastructure.

The St. Mary Diversion can provide up to 90% of the Milk River flow during irrigation season. Approximately 140,200 acres of land are irrigated between irrigation districts, individual pump contracts, and private state water rights holders. The US Bureau of Reclamation has contracts to provide irrigation for 110,000 acres.

The St. Mary diversion was designed to carry 850 cfs (cubic feet/second) and currently carries 670 cfs due to the condition. There are five drops in the dievrsion system and the drops are experiencing deterioration. The siphons that were hand riveted during their construction contain leaks which contribute to the inefficiency of the system. Annual water shortages in the Milk River have been recorded and the rehabilitation of the structures would reduce the shortages that occur.

siphon leak

The St. Mary’s Rehabilitation Working Group hired Thomas Dean & Hoskins (TD&H) in 2005 to provide a rehabilitation work plan for the conveyance systems. The St. Mary’s system rehabilitation is roughly estimated at $200 million. The original estimate was produced in 2004 and the current estimate includes inflation and additional allowances for species impacted by the structures. This includes a fish ladder for the Bull Trout which was listed as a threatened species in 1998 by the U.S. Fish and Wildlife Service.

Failure to act on the rehabilitation of the system could lead to the failure of the system. This poses economic and environmental disaster to the Hi-Line. Stakeholders of the Milk River that would be adversely affected include irrigation districts and private irrigators, the municipalities of Havre, Chinook, an Harlem, First Nations Tribes, fisheries, ranchers, farmers, businesses, and various recreation and wildlife groups. Endangered or threatened species like the Pallid Sturgeon, hydro-power produced by project facilities, and the Fort Belknap and Blackfeet water compacts will all be affected by failure since they are reliant on the diverted water.


St Mary and Milk River Project Story Map

Click the link above to view an interactive and user friendly story map of the St Mary Diversion and Milk River Project!