Mousam River

"Statewide ecological significance"

The main stem of Mousam River is 24 miles long from its source at Square Pond in Shapleigh, to its mouth in Kennebunk. The river consists of three main tributaries: the main stem, Littlefield River, and the Middle Branch of the Mousam. It reaches the Atlantic in Kennebunk between Parsons Beach and Kennebunk Beach.


Drainage: 122 square miles
Drinking water source for: None
Receives wastewater from: Sanford
Significant water features: Estes Lake, Mousam Lake, Parsons Beach, Square Pond

Watershed Description

The Mousam River Watershed drains portions of Acton, Shapleigh, Waterboro, Sanford, Alfred, Lyman, and Kennebunk, Maine. The western portion of the watershed is largely rural, with thousands of acres of wetlands, forests, and agricultural lands. Development near the headwaters of the Mousam River is concentrated along the shores of the lakes and ponds and the densest development occurs around the river as it passes through the center of Sanford. In this area, an extremely high percentage of impervious surface causes increased flows of stormwater to the river. In the eastern region of the watershed, Middle Branch is surrounded by agricultural and forested lands as well, with dense development occurring near the town centers of Waterboro and Alfred.

Several parcels of conservation land are located throughout the watershed, particularly in the lower portion, including state and federally managed lands as wells as privately held easements. The extensive wetlands and forested lands in the upper portions of the watershed consist of scattered areas of significant habitat for a variety of wildlife, including waterfowl and wading birds, the endangered northern black racer, the ringed boghunter,  the endangered Blanding's turtle, and the endangered spotted turtle. The river passes through an extensive tidal estuary area as it reaches the Atlantic, which functions as important habitat for shorebirds and the endangered Piping Plover.

Due to the extensive undeveloped land found within the watershed, the Mousam river is described as being of "statewide ecological significance". However, it is currently one of the most heavily dammed rivers in the state, which has inhibited the life cycles of sea-run species including Atlantic salmon and alewives. Many of the dams provide hydro-electrical power and their removal is heavily debated by local stakeholders. 

Local Information

Towns in Watershed

Acton, Alfred, Kennebunk, Lyman, Sanford, Waterboro

Three Rivers Land Trust

Three Rivers Land Trust was founded in 2000 by a small group concerned about the sale of thousands of acres in the area that were subsequently developed into house lots. Since then, they have worked to maintain, support and enhance the working landscape of  farms and forest and such valued natural resources as lakes, rivers, streams, wetlands, historic sites, scenic places and wildlife habitat by acquiring property in fee and conservation easements, and by garnering community support.

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