The northwest side of Caribou Mountain drains into the West Branch of the Moose River, thence into the South Branch of the Moose, the Moose River, and the Kennebec River, then into the Gulf of Maine. The southeast side of Caribou Mountain drains into Number Six Brook, then into the South Branch of the Moose River. The southwest end of Caribou Mountain drains into Rivière aux Araignées in Saint-Augustin-de-Woburn, Quebec, then into Lac aux Araignées, Lac Mégantic, the Rivière Chaudière, the Saint Lawrence River, and into the Gulf of Saint Lawrence.