The Thomsen River, located in the Northwest Territories

Northwest Territories

The Northwest Territories is a federal territory of Canada.Located in northern Canada, the territory borders Canada's two other territories, Yukon to the west and Nunavut to the east, and three provinces: British Columbia to the southwest, and Alberta and Saskatchewan to the south...

 of Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, is the northernmost usable river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 of the country. It is famous for canoe

Canoe

A canoe or Canadian canoe is a small narrow boat, typically human-powered, though it may also be powered by sails or small electric or gas motors. Canoes are usually pointed at both bow and stern and are normally open on top, but can be decked over A canoe (North American English) or Canadian...

ing.

It flows across Banks Island

Banks Island

One of the larger members of the Canadian Arctic Archipelago, Banks Island is situated in the Inuvik Region of the Northwest Territories, Canada. It is separated from Victoria Island to its east by the Prince of Wales Strait and from the mainland by Amundsen Gulf to its south. The Beaufort Sea lies...

 in the Canadian Arctic Archipelago

Canadian Arctic Archipelago

The Canadian Arctic Archipelago, also known as the Arctic Archipelago, is a Canadian archipelago north of the Canadian mainland in the Arctic...

, and flows northward through Aulavik National Park

Aulavik National Park

Aulavik National Park is a national park located on Banks Island in the Northwest Territories of Canada. It is known for its access to the Thomsen River, one of the most northerly navigable rivers in North America. The park is a fly-in park, and protects approximately of Arctic Lowlands at the...

 before it empties through the Castel Bay

Castel Bay

Castel Bay is a Canadian Arctic waterway in the Northwest Territories. It is a southern arm of M'Clure Strait on northeast Banks Island. The mouth of the larger Mercy Bay is less than to the east. These bays are a part of Aulavik National Park....

 into the M'Clure Strait (part of the Viscount Melville Sound

Viscount Melville Sound

Viscount Melville Sound is an arm of the Arctic Ocean in Kitikmeot, Nunavut, Canada. Forming part of the Parry Channel, it separates Victoria Island and Prince of Wales Island from the Queen Elizabeth Islands. East of the sound lies Lancaster Sound, leading into Baffin Bay; westward lies the...

 of the Arctic Ocean

Arctic Ocean

The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...

).

The Thomsen River on northern Banks Island has been described as the most northerly multi-species river in North America. At least three fish species, Lake Trout (Salvelinus namaycush), Least Cisco (Coregonus sardinella) and Ninespine Stickleback (Pungitius pungitius), reach their known northern limit of distribution in the Thomsen River while the Arctic char (Salvelinus alpinus) is a common species. Lake whitefish (Coregonus clupeaformis) may also occur in upper reaches of the Thomsen and marine Fourhorn sculpin (Myoxocephalus quadricornis) are occasionally found in the lower reaches of the river. Approximately one half of the Thomsen River watershed lies within Aulavik National Park.