The Sumas River is a tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Fraser River

Fraser River

The Fraser River is the longest river within British Columbia, Canada, rising at Fraser Pass near Mount Robson in the Rocky Mountains and flowing for , into the Strait of Georgia at the city of Vancouver. It is the tenth longest river in Canada...

 in the Canadian province

Provinces and territories of Canada

The provinces and territories of Canada combine to make up the world's second-largest country by area. There are ten provinces and three territories...

 of British Columbia

British Columbia

British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

 and the U.S. state

U.S. state

A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...

 of Washington.

Course

The Sumas River originates in Whatcom County, Washington

Whatcom County, Washington

Whatcom County is a county located in the U.S. state of Washington. Its name ultimately derives from the Lummi word Xwotʼqom, meaning "noisy water." As of 2010, the population was 201,140. The county seat is at Bellingham, which is also the county's largest city...

 just north of the Nooksack River

Nooksack River

The Nooksack River is a river in the northwest part of the U.S. state of Washington. It drains an area of the Cascade Range around Mount Baker, near the Canadian border. The lower river flows through a fertile agricultural area before emptying into Bellingham Bay and, via the Strait of Juan de Fuca...

 and west of Sumas Mountain

Sumas Mountain

Sumas Mountain is a mountain located in Whatcom County, Washington, 15 miles northeast of Bellingham and southwest of Vedder Mountain. Located in the Skagit Range the mountain is notable for its high biodiversity and year-round hiking trails. It is sometimes referred to as American Sumas to...

. It flows generally northeast, crossing the Canada–United States border and emptying into the Fraser River.

Swift Creek, a tributary of the Sumas River, is contaminated with naturally occurring asbestos

Asbestos

Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

-laden sediment from the slow-moving Swift Creek Landslide

Swift Creek Landslide

The Swift Creek Landslide is an active, slow moving landslide located in western Washington, USA, due east of Everson on Sumas Mountain. Asbestos laden sediment originating from the landslide has recently generated much interest in this area...

.

History

The Sumas River used to flow into Sumas Lake

Sumas Lake

Sumas Lake was a body of water between Sumas and Vedder mountains, midway between the present-day cities of Chilliwack and Abbotsford, British Columbia. Its name means "a big level opening" and is a reference to the site of the lake, which lay between Sumas Mountain and its American counterpart,...

, a large lake on the Fraser River's floodplain. In the 1920s the lake was drained.