The Souris River or Mouse River (as it is alternatively known in the U.S.) is a river in central North America. It is about 700 km (435 mi) in length and drains about . It rises in the Yellow Grass Marshes north of Weyburn, Saskatchewan. It wanders south through North Dakota beyond Minot to its most southern point at the city of Velva, and then back north into Manitoba. The river passes through the communities of Melita, Hartney, Souris and Wawanesa and on to its confluence with the Assiniboine River at Treesbank, about south east of Brandon. The main tributaries which flow into the Souris in Manitoba are the Antler River, the Gainsborough and Plum Creeks. Much of its drainage basin is fertile silt and clay deposited by former glacial Lake Souris.