The lake is the farthest upstream of the five headwater lakes of the Salmon Falls River, a tributary of the Piscataqua River. Water from Great East Lake flows out its dam and through the  Newichawannock Canal into Horn Pond, then into the Salmon Falls River below Horn Pond.
The lake is the most upstream of the five headwater lakes in the Salmon Falls River, a tributary of the Piscataqua River. Water from Great East Lake flows out its dam and through the Newichawannock Canal into Horn Pond, then into the Salmon Falls River below Horn Pond.