St. Mary Diversion Dam

The St. Mary Diversion Dam and Canal were completed in 1915 as part of the Milk River Project (Project) in north-central Montana. The dam is located near Babb, MT and approximately 0.75 miles downstream from Lower St. Mary Lake. The existing dam consists of a 198-foot long and 6-foot-high concrete weir and sluiceway. It diverts water from the St. Mary River into the St. Mary Canal through the gated headworks structure for use by the Milk River Project in accordance with the Boundary Waters Treaty division of waters between the U.S. and Canada assuring water supply and viability of irrigated agriculture on the Milk River Project. Much of the dams existing structural components are dilapidated and in need of replacement.

The St. Mary Diversion Dam Replacement Project will include all activities required to design, construct, and closeout construction of a new diversion dam and fish protection structure that will comply with the Endangered Species Act (ESA). The main features of the project will be a low head diversion dam and rock ramp for upstream passage, a new headworks structure, a canal fish screen, a check structure downstream of the fish screen, a fish bypass to return fish to the river, O&M and control buildings, and auxiliary features.

The Infrastructure Investment and Jobs Act (IIJA) has set aside $100M directed to facilities that have failed in the last two years, in a way that prevented delivery of water for irrigation. As written, the St. Mary Diversion Dam and Canal is the only project to fit these criteria. The $100M does not require reimbursement by the Milk River Project water users and will be used to fund the replacement of the St. Mary Diversion Dam and Headworks.

The primary stakeholders on the Project are the Blackfeet Nation, the U.S. Fish and Wildlife Service, and the eight irrigation districts that make up the Milk River Irrigation Project Joint Board of Control (Joint Board). Other stakeholders include over 150 pumpers along the Milk River and six municipal entities.

Project Overview & Contact Information

Contact Project Manager:
Steve Darlinton  – Project Manager
(406) 247-7322
Bureau of Reclamation
Montana Area Office
PO Box 30137 Billings, MT 59101
(406) 247-7300

Document Vault

St. Mary Diversion Dam Biological Opinion from US Fish & Wildlife Services

September 2020

St. Mary Biological Assessment 2020


April 2020

2022 Geologic Investigation & Design Report 



April 2023