Project Info

Mansfield Hollow Dam lies on the confluence of the Natchaug, Fenton, and Mt. Hope Rivers, in Mansfield, Connecticut. The dam is part of a network of six flood risk management dams in the Thames River Basin constructed and maintained by the U.S. Army Corps of Engineers New England District. This network helps to reduce flooding in communities within the Thames River Basin by regulating water levels on upstream tributaries in Connecticut and Massachusetts. The project provides substantial flood protection for the Shetucket River communities of Norwich, South Windham, Baltic, Occum, Taftville, and Willimantic. The lake lies within the boundaries of Mansfield and Windham, 25 miles east of Hartford.

Construction of the dam began in 1949 and was completed in May 1952. The cost of the project was $6.5 million. The dam consists of earthfill with stone slope protection. It has a length of 14,050 feet and a height of 68 feet. The project also consists of six earthfill dikes with stone slope protection that total 2,656 feet in length and have a maximum height of 53 feet.  The project offers recreational opportunities compatible with the primary function of flood risk management.

While the main purpose of Mansfield Hollow Lake was to provide flood risk management to the Thames River Basin, over the years the lake has become a recreational draw due to its location and beautiful natural surroundings. With over 15 miles of trails, 2,472 acres of land, 450 acres of water, picnic areas, and a boat launch, the lake can accommodate all kinds of outdoor enthusiasts.

The U.S. Army Corps of Engineers owns 2,472 acres, of which the State of Connecticut Department of Energy and Environmental Protection leases approximately 2,300 acres for recreation and natural resource management. On a graceful, pine-covered bluff overlooking the broad expanse of water, a picnic shelter and individual picnic sites for both families and large groups are available at the Mansfield Hollow State Park. Many acres of open field lie adjacent to the bluff and may be used for softball, touch football, volleyball, and other team sports and group activities.

Fish species observed in the lake include black crappie, pumpkinseed and bluegill sunfish, largemouth and smallmouth bass, yellow perch, brown bullhead, chain pickerel, white sucker, American eel, golden shiner, carp and rainbow, brook, and brown trout. Northern pike are also present, having been reintroduced to the lake in 1992.

All project lands and waters are under the jurisdiction of CFR Title 36 regulations, state and local laws.

The U.S. Army Corps of Engineers is updating the Mansfield Hollow Lake Master Plan. The Master Plan is the strategic land use management document that guides the comprehensive management and development of all project resources throughout the life of a USACE project. The Master Plan guides efficient and cost-effective management, development, and use of project lands.  It is a vital tool for the responsible stewardship and sustainability of project resources for the benefit of present and future generations. The Master Plan guides and articulates USACE responsibilities, pursuant to federal laws to preserve, conserve, restore, maintain, manage, and develop project lands and waters and associated resources. The intent of an updated Master Plan is to present a current inventory and assessment of resources, provide an analysis of resource use, and evaluate existing and future needs required to protect and improve the value of resources at a project.

The current Mansfield Hollow Lake Master Plan, last approved in 1979, needs revision to address changes in regional land use, population, outdoor recreation trends, and the USACE management policy. Key topics to be discussed in the revised Master Plan include revised land use classifications, new natural and recreational resource management objectives, recreation facility needs, and special issues such as invasive species management and threatened and endangered species habitat. The Master Plan revision WILL NOT address the technical and operational aspects of the lake related to flood risk management or the water conservation missions of the project. During the process, the team will collect data, conduct analysis, prepare a draft report (which will become available for public and agency comments), and ultimately finalize and adopt the new Master Plan.

The U.S. Army Corps of Engineers (USACE) will host an open house on Thursday, May 2, 2024, from 4 - 6 p.m. at the Mansfield Public Library Programming Room, to share details on a draft revision process of the Mansfield Hollow Lake Master Plan and showcase the existing land use classification maps, which are original from 1979.  A 30-day public comment period began on May 3, 2024, and will end on June 1, 2024.

Public Comment

A 30-day comment period will begin May 2, 2024, and end June 1, 2024. The public can send comments, suggestions, and concerns during this time. Comments must be submitted in writing at the open house or digitally via email by contacting