The Dease River flows through northwestern British Columbia, Canada and is a tributary of the Liard River. The river descends from Dease Lake, though its ultimate origin is in the headwater of Little Dease Creek at Snow Peak, approximately 50 km to the west of the lake. The river flows 265 km generally north-eastward, draining into the Liard River near Lower Post, British Columbia. Large sections of the river parallel the Cassiar Highway, helping to make it a popular destination for canoeists, kayaakers, and rafters.
The area has a rich history. It is important to the history of Tahltan and KaskaFirst Nations, who continue to reside along the river. The first European known to have visited the river was John McLeod, a Hudson's Bay Companyfur trader and explorer, in August 1831. He named the river for Peter Warren Dease, at the time Chief factor of the Mackenzie River District of the Hudson's Bay Company. In 1837, Robert Campbell established a Hudson's Bay Company fur trading post at Dease Lake. The community of Dease Lake has a population of approximately 650, and is the major centre in the river's watershed.