Most, but not all, watersheds drain into rivers and, ultimately, the ocean. A closed watershed, or an endorheic basin, however, retains its water. The water that falls within it leaves only by evaporation or seepage.
The Aral Sea and the Caspian Sea are part of a closed drainage basin. Canada has a few closed watersheds in British Columbia, Alberta and Saskatchewan. Little Manitou Lake in Saskatchewan is part of a closed watershed. Because of the minerals and salts left behind when the water evaporates, the lake has become incredibly salty over time— it is five times saltier than the ocean. Old Wives Lake in Saskatchewan and Pakowki Lake in Alberta are also closed watersheds.
British Columbia's Spotted Lake, one of several closed watersheds in the province, contains very high concentrations of minerals and salts.