Watersheds

Dark Green: the Merrimack River watershed
Blue: Water
Red Lines: Location of Dams

A watershed is the area over which water pools and empties into a larger body of water, like a river or stream. The Merrimack River watershed runs across two states, beginning around Lake Winnepesaukee in central New Hampshire and ending at the Atlantic Ocean off the Massachusetts coast. This 117 mile long river does not have an endless water supply from Northern lakes - it also receives water from tributaries (other rivers that flow into the Merrimack), rainfall, and groundwater.

During the American Industrial Revolution, the Merrimack's water was used to fuel industry in the city of Lowell, turning massive waterwheels that could power entire factories with the strength of the river. To maximize profit, mill agents and engineers installed a dam to retain water, diverting it from its natural flow and pushing it through the canals instead.

Damming the river backed up a significant amount of water upstream, flooding local farms and riverbanks on which animals and plants relied. This disrupted the watershed, which typically kept a cyclical track - water flows into the Merrimack, is deposited into the ocean, evaporates as part of the water cycle, and returns as rain to the watershed.

While these dams also backed up water, they also blocked out fish. Migratory species like the Atlantic salmon, shad and alewives need to get from the Atlantic Ocean to fresh waters in northern New Hampshire to lay their eggs, but their path is blocked by the dams. While some fish ladders were constructed to help them climb the falls, the fish's population continued to decline.