The Watertown Dam spans the Charles River 980 feet (300 m) upstream from the Watertown Bridge near Watertown Square in the Town of Watertown, Massachusetts where the Charles River tidal estuary ends. Watertown Dam is of earthen construction, a gravity dam. Its length is 220 feet. Its capacity is 30 acre feet. Normal storage is 20 acre feet. It drains an area of 0.2 square miles.

The history of the dam traces back to 1632 when construction of a fish weir was authorized. The current dam, maintained by the Department of Conservation and Recreation, dates from 1900.