Lake Sebago, at 310 acres, is the biggest lake in Harriman State Park. It’s name supposedly means “big water” in Algonquin, though Wikipedia didn’t indicate which Algonquin language that was. My guide books don’t include that information either. Hopefully it’s from the Lenape language since they lived in the area prior to the Europeans arriving.
On the other hand, Lake Sebago didn’t exist in precolonial times. It was created in 1925 by damming a section of Stony Brook, flooding the former logging community of Johnsontown, which had been condemned by the Palisades Interstate Park Commission and torn down a few years earlier. Maybe they should have named it Lake Eminent Domain.