At approximately 250 kilometres (160 mi), it is one of Nova Scotia's longest rivers.

[1] The river drains an area of approximately 1,350 square kilometres (520 sq mi) and has four branches; the West, East, North and Main.

Named Rivère Isle Verte by explorer Samuel de Champlain,[4] the current name is from Fort Saint Marie, a French-built fort which was later taken over and destroyed by the British.

Atlantic salmon, an endangered species, inhabit the river.

[3] There are efforts under way by the Nova Scotia Nature Trust to protect ecologically important lands along the river.