High Quality Content by WIKIPEDIA articles! The Songo River is a 3.1-mile-long (5.0 km) river in Maine with the only remaining operational lock of the Cumberland and Oxford Canal. The river flows from Brandy Pond at the south end of Long Lake into Sebago Lake at Sebago Lake State Park. Songo Lock controls the elevation of Long Lake and allows navigation of large boats between Long Lake and Sebago Lake.