The canal lock system provided elevation control of the 45-square-mile (117 km2) surface area of Sebago Lake as a reservoir for water-powered mills along the river. The S. D. Warren Paper Mill in Westbrook vied with the Oriental Powder Company in Gorham and Windham to control water flow after the canal ceased operation of the locks. The paper mill exercised control for more than half a century after the gunpowder factory closed in 1905.[10]