Our Watershed

We all have one thing in common: no matter where we live, we all live in a watershed.

A watershed (also known as a drainage basin, river basin or catchment) is an area of land that catches precipitation and drains into a larger body of water such as a river or lake. The boundaries of a watershed are defined by the height of land of the elevation divide separating one watershed from another.

Total Area of the Milk River Watershed

61,642 km2

(23,800 sq mi)

Area of Watershed in Canada

21,442 km2

(8,442 sq mi)

Area of Watershed in Alberta

6,500 km2

(2,510 sq mi)

Area of Watershed in Montana

40,199 km2

(15,521 sq mi)

Length of Milk River

1,173 km

(700 miles)

Number of Tributaries


Irrigated Land in the Watershed

3,300 ha

(8,154 acres)

A Transboundary Watershed

The Milk River watershed spans an area of 59,857 km2 (5,985,653 ha; 14,790,813 acres) in Alberta, Saskatchewan and Montana. The Milk River and its tributaries intricately connect the two provinces and the state as they share similar experience with climate, water quantity, water quality and other aspects of the ecosystem.

There are 480 km (298 mi) of shared international border between Canada and the United States. The mainstem Milk River rises in the grasslands of Montana and flows northward into Alberta before flowing eastward a distance of about 288 km (179 mi) parallel to the Canada-United States border. The river then flows south and returns to Montana where it flows through Fresno Reservoir and continues to flow southeast a distance of 710 km (441 mi) before joining the Missouri River. The Milk River Watershed is the only watershed in Canada that drains to the Gulf of Mexico.

Topographic Limits

The topographic limits for the watershed are the Rocky Mountains on the Blackfeet Reservation in the west, Montana, the Milk River Ridge that extends from the Rocky Mountains northeastward in Alberta, to the Cypress Hills, (Alberta and Saskatchewan) and Wood Mountains in the north (Saskatchewan). The Sweetgrass Hills, Bears Paw and Little Rocky Mountains form the limit in the south (Montana). Elevations vary considerably in the watershed from west to east and reflect topographical features. The highest peak is found in the west at Glacier National Park in the Rocky Mountains (2,663 m or 8,737 ft) and the lowest elevation is located at the confluence of the Milk and Missouri rivers (619 m or 2,031 ft). At the point where the Milk River flows across the Canada-United States border, the elevation is 819 m (2,687 ft), the lowest elevation in southern Alberta.


Important tributaries include the North Fork of the Milk River which is often mistaken for the mainstem Milk River as it generally contains higher flows that are sustained by the St. Mary River Diversion in Montana. From the Canada-United States border, the North Fork flows a distance of 96 km (60 mi) before meeting the mainstem of the Milk River west of Del Bonita, Alberta. In Saskatchewan, substantial flows are delivered to the Milk River via three major tributaries: Lodge Creek, Battle Creek and the Frenchman River, which originate in the Cypress Hills. Lodge Creek and Battle Creek flow south across the Saskatchewan-Montana border and continue to flow south into the Milk River near Chinook, while the Frenchman River joins the Milk River further downstream near Hinsdale, Montana.

Watershed Maps

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Irrigated areas within the Milk River transboundary watershed as of 2013.

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Land ownership within the Milk River transboundary watershed as of 2013.

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Land cover within the Milk River transboundary watershed as of 2013.

Explore more features and history of the watershed through the interactive Story Map.

Quick Facts

Where does the name of the watershed come from?

On May 8, 1805, Meriweather Lewis wrote in his journal: “The water of this river possesses a peculiar whiteness, being about the colour of a cup of tea with the admixture of a tablespoon of milk. From the colour of its water, we called it the Milk River.
(Journals of the Lewis & Clark Expedition, University of Nebraska)

Where does our water come from?

On average 80-90% of the river flow of the Milk River comes from a diversion off the St Mary’s River in Montana. If not for the St Mary’s diversion, most years late summer natural flow of the Milk River east of the Town of Milk River would be non-existent.

Groundwater and Milk River flow

Studies have demonstrated the connectivity of the Milk River to both the Whiskey Valley Aquifer and the Milk River aquifer. Over 350 farms, acreages, and parks are reliant on Water Co-ops that draw from the Milk River and adjacent aquifer for domestic drinking water. Thanks to the leadership of the MRWCC and Geological Survey of Canada, we have some of the best transboundary aquifer mapping resources in the world right here in Milk River.

Water quality of the Milk River is affected by the St Marys River

The MRWCC has been monitoring water quality along the Milk River and many important tributaries for over 10 years. This data has helped form some of the most complete long term trend data sets found in any of the province’s major watersheds. Trends have shown us there are distinct differences in water quality between the Milk River natural flow which is high in salts and influenced by springs/groundwater flows; and St Marys River which is often higher in quality and glacial fed. The Milk River is distinctly two different rivers between the diversion and non-diversion periods.   

Water and agriculture

There are over 93,000 acres of irrigation reliant on the Milk River throughout the highline of Montana, and on average 8600 acres in Alberta. The Milk River is just as valuable to the ranching community with thousands of head of livestock reliant on the Milk River for water sources, rich riparian plains for grazing and refuge. 

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Land, Water, and People

Trends in human population are often cited as an indicator of watershed health as they describe the social “quality of life” aspect of watersheds. In many watersheds in North America, urbanization is occurring rapidly, resulting in land use changes from a rural landscape to more centralized urban centres. The Milk River watershed remains rural and the total population is relatively small. In Alberta, the total population in the watershed is 2,534, showing a -9.1% population decline since 2008.

The Milk River provides water for various purposes such as municipal, domestic, agricultural and recreational activity; however, irrigation is the main water use across the watershed. Since the Milk River is considered an arid basin (meaning that evaporation exceeds precipitation), various storages and diversions are operated in the watershed mainly in Saskatchewan and Montana to meet irrigation demand. Such infrastructure is not available in the Alberta portion of the Milk River; however the St. Mary River Diversion augments Milk River natural flows during the irrigation season, typically from the beginning of March to the end of October.

The natural flow of the Milk River in Alberta in winter months is low and may approach zero in the lower reaches in times of drought. Flow depths across the channel width can be less than 0.1 m, limiting the movement of larger fish and increasing the potential for isolated pools that are disconnected from the main channel (Golder Associates 2010; AMEC Earth and Environmental 2011).