The Sebago Lake drainage basin includes the Crooked River draining Songo Pond south of Bethel, and the Bear River from Waterford through Long Lake. The basin is between the Saco River drainage basin to the west and the Androscoggin River drainage basin to the north and east. In addition to Sebago Lake's being its primary source, four significant tributaries of the river are the Pleasant River from Gray through Windham, the Little River from Buxton through Gorham, Mill Brook in Westbrook (which is an outlet of Highland Lake in Windham), and the Piscataqua River in Falmouth (which is an outlet of Forest Lake in Cumberland).