Union River
The Union River in Ellsworth, Maine
CountryUnited States
Physical characteristics
 • locationMaine
 • location
Union River Bay
 • coordinates
44°28′48″N 68°25′55″W / 44.480°N 68.432°W / 44.480; -68.432
 • elevation
sea level
Length22 miles (35 km)
Basin features
 • leftEast Branch Union River,
Webb Brook
 • rightWest Branch Union River

The Union River is a 21.9-mile-long (35.2 km)[1] river that runs through Ellsworth, the county seat of Hancock County in eastern Maine. In the colonial era, it was known as the Mount Desert River.[2]

The river forms at the north end of Graham Lake at the confluence of the river's East and West branches (44°43′48″N 68°23′04″W / 44.7300°N 68.3844°W / 44.7300; -68.3844 (Union River source)), on the border of the towns of Mariaville and Waltham. It runs south 13 miles (21 km) through Graham Lake to the dam at the lake's outlet, then continues south through Ellsworth, flowing through Leonard Lake and passing over its outlet dam just above the downtown. The Leonard Lake dam, also known as The Ellsworth Dam, built in 1907, spans the Union River and forms Lake Leonard. It houses a powerhouse with four generating units that combined produce 29,907 megawatt hours per year, enough to power about 3,000 households. At downtown Ellsworth, the river reaches tidewater, and flows south as an estuary for 5 miles (8 km) to its mouth at Union River Bay, on the border of Surry and Ellsworth, and thence into Blue Hill Bay.


  1. ^ U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National Map Archived 2012-03-29 at the Wayback Machine, accessed June 22, 2011
  2. ^ Maine League of Historical Societies and Museums (1970). Doris A. Isaacson (ed.). Maine: A Guide 'Down East'. Rockland, Me: Courier-Gazette, Inc. p. 344.