The Rainy River Basin
The basin may be considered as three distinct sub-basins as follows:
Namakan Lake sub-basin, which includes the Namakan Chain of Lakes (Namakan Lake, Lake Kabetogama, Crane Lake, Sand Point Lake, and Little Vermillion Lake) which have water levels influenced by the dam operations at the outlet of Namakan Lake) and upstream lakes and rivers, the largest of which are Lac La Croix and Basswood Lake;
Rainy Lake sub-basin, which receives tributary flows from the Namakan Lake sub-basin as well as flows from the Seine River watershed and the Turtle River.
Rainy River sub-basin, which receives all flow out of Rainy Lake in addition to a sizeable watershed that includes the Big Fork and Little Fork rivers in Minnesota and additional drainage from smaller tributaries in Ontario. Rainy River is the boundary between Canada and the United States from Rainy Lake to Lake of the Woods.