The river begins at an unnamed lake in geographic Fabbro Township.

The Mississagi River flows to the North Channel on Lake Huron.

Additionally it includes the entire West Little White River and its headwater lakes (such as Pointer, Finn, Town Line, Robb, Elbow, Kirkpatrick, White Bear, and Endikai Lakes), as well as Raven Lake Uplands that stretches to the Wakomata portion of the Mississagi River Provincial Park.

[5][6][7] Features in the park include wetlands, oxbow sloughs, and floodplain swamps with stands of silver maple, black ash, and white elm.

The Raven Lake natural heritage area contains bedrock cliff faces, upland rock barrens, deep gorges, ravines, convoluted linear wetlands, and significant stands of white pine growing on the glacier-scoured hills.