Lake Monomonac is an artificial lake that straddles the border between Rindge, New Hampshire

Rindge, New Hampshire

Rindge is a town in Cheshire County, New Hampshire, United States. The population was 6,014 at the 2010 census. Rindge is home to Franklin Pierce University, the Cathedral of the Pines, and part of Annett State Forest.-Native American inhabitants:...

 and Winchendon, Massachusetts

Winchendon, Massachusetts

Winchendon is a town in Worcester County, Massachusetts, USA. The population was 10,300 at the 2010 census. Home to Winchendon State Forest, the town includes the villages of Waterville and Winchendon Springs....

. It was created from a small pond in New Hampshire

New Hampshire

New Hampshire is a state in the New England region of the northeastern United States of America. The state was named after the southern English county of Hampshire. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Atlantic Ocean to the east, and the Canadian...

 by the construction of dams on the North Branch of the Millers River

North Branch Millers River

The North Branch of the Millers River is a river in southwestern New Hampshire and northern Massachusetts in the United States. It is a tributary of the Millers River, which flows west to the Connecticut River, which in turn flows south to Long Island Sound, an arm of the Atlantic Ocean.The North...

, a part of the Connecticut River

Connecticut River

The Connecticut River is the largest and longest river in New England, and also an American Heritage River. It flows roughly south, starting from the Fourth Connecticut Lake in New Hampshire. After flowing through the remaining Connecticut Lakes and Lake Francis, it defines the border between the...

 watershed

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

.

Lake Monomonac is 594 acres (240.4 ha) in size with 410 acres (165.9 ha) in New Hampshire and the remaining 184 acres (74.5 ha) in Massachusetts. The lake has a maximum recorded depth of twenty-five feet and an average depth of ten feet.