Was this Lake Grove Park in Auburn ?? I believe Lake Grove Park was on a LAKE while this speaks of the river that flows through Lewiston.

The Presumpscot River, flowing to the ocean, provided a beautiful backdrop for the small stage. Lake Grove Park in Lewiston,Maine, was on the well known J.W.Gorman booking circuit...-THEATER IN AMUSEMENT PARKS--- (the reference source..date and publisher unknown)