# Milk River (Alberta–Montana)

Milk River is a tributary of the Missouri River, 729 miles (1,173 km) long, in the U.S. state of Montana and the Canadian province of Alberta. Rising in the Rocky Mountains, the river drains a sparsely populated, semi-arid watershed of 23,800 square miles (62,000 km$^2$), ending just east of Fort Peck, Montana.

## Geography

It is formed in Glacier County in northwestern Montana, 21 miles (34 km) north of Browning, Montana, by the confluence of its South and Middle forks. The 30-mile (48 km) long South Fork and 20-mile (32 km) long Middle Fork both rise in the Rocky Mountains just east of Glacier National Park, in the Blackfeet Indian Reservation. Much of the water in the North Fork is diverted from the St. Mary River through a canal and inverted siphon.
The main stream flows east-northeast into southern Alberta, where it is joined by the North Fork of the Milk River, from there It flows past the town of Milk River and Writing-on-Stone Provincial Park, then turns southeast into Montana, running east along the north side of the Sweetgrass Hills, turning south, passing through the Fresno Dam, then east past Havre and along the north side of the Fort Belknap Indian Reservation. Near Malta, it turns north, then southeast, flowing past Glasgow and joining the Missouri in Valley County, Montana, 5 miles (8 km) downstream from Fort Peck Dam.
The watershed of the river extends into the Canadian provinces of Alberta and Saskatchewan and the US state of Montana. The watershed of the river covers an area of 61,642 km$^2$ (23,800 sq mi). Of this 6,500 km$^2$ (2,510 sq mi) lies in Alberta, 14,942 km$^2$ (5,769 sq mi) in Saskatchewan and the remaining in Montana. The area in Alberta and Saskatchewan is one of the few parts of the Mississippi River watershed that extends into Canada.
| River | Location | Discharge |
| North Fork Milk River | US-Canada Border | 99 cu ft/s (2.8 m$^3$/s) |
| South Fork Milk River | near Browning | 98 cu ft/s (2.8 m$^3$/s) |
| Milk River | Nashua | 618 cu ft/s (17.5 m$^3$/s) |

## History

The Milk River was given its name by Captain Meriwether Lewis, of the Lewis and Clark Expedition, who described the river 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 full of milk. from the colour of its water we called it Milk river.
This appearance results from clays and silts suspended in its waters. These fine-grained sediments result from the erosion of soft clay-rich rocks along the Milk River basin in southern Alberta, such as the Foremost, Oldman and Dinosaur Park formations.
At the time of Lewis's exploration, the Milk River drainage was legally part of the United States as a component of the Louisiana Purchase. However, in 1818 U.S. negotiators swapped a portion of the Milk River watershed that lay north of 49° north latitude, receiving in exchange for a parcel of Red River of the North drainage that had previously been part of British North America.
The project to take water from St. Mary River into the north fork was authorized in 1905. It provides drinking water to 14,000 municipal users and irrigation to 120,000 acres (49,000 ha) of ranchland along Montana’s Hi-Line region. In 1908, the waters of the Milk River were the subject of a United States Supreme Court case clarifying the water rights of the Fort Belknap Indian Reservation. This precedent setting ruling for Indian reservations is known as Winters v. United States.

## Habitat

The Milk River area consists of three drainage basins – the Lost River Valley to the northeast, the Milk River in the middle, and the Kennedy Coulee to the southeast. The landscape consists of native grasslands, riparian cottonwood groves, badlands, coulees, cliffs, sand dunes, and rocky outcrops. Birds in the area include the mountain plover, burrowing owl, sage grouse, loggerhead shrike, Sprague's pipit, long-billed curlew, ferruginous hawk, prairie falcon, willet, marbled godwit, lark bunting, Baird's sparrow, McCown's longspur, and the chestnut-collared longspur. The area also supports pronghorns, western hognose snakes, bull snakes, prairie rattlesnakes, and northern leopard frogs.