The Betsie River is a 54.0-mile-long (86.9 km) stream in the northwest part of the U.S. state of Michigan. The name is derived from the French la rivière aux Bec-scies, meaning river of sawbill ducks (bec-scie). Other alternate names include Aug-sig-o-sebe, Aux Buscies, Betsey's River, Black Robe, Gay-she-say-ing, Riviere du Pere Marquette, Sawbill Ducks, and Shelldrake Ducks. The river is mostly within Benzie County (which takes its name from a variant pronunciation of the river), although the river rises in southwest Grand Traverse County and flows briefly through northern Manistee County, Michigan.
The river widens to form Betsie Lake before emptying into Lake Michigan at 44°37′45″N 86°14′45″W / 44.62917°N 86.24583°W between Frankfort and Elberta. The Betsie River is a part of Michigan's Natural Rivers Program.
While most sources indicate the river rises as the outflow of Green Lake at 44°35′31″N 85°47′40″W / 44.59194°N 85.79444°W in southwestern Grand Traverse County, some consider it navigable immediately south of US-31 from Tuller's Lake to Green Lake. Green Lake straddles the boundary between Grant Township on the south and Green Lake Township on the north between Karlin and Interlochen. Several nearby lakes, including Duck Lake and its tributaries, drain into Green Lake.