Dam in Fitchburg, MA

River Continuity: Dams and Culverts

Our rivers and streams once flowed naturally and freely through the landscape. Human development necessitated the building of dams to control water supplies and harness their power. Road construction for our transportation systems meant stream crossings, frequently accomplished by the use of culverts rather than bridges. These interruptions to the natural flow of the river impact aquatic life, and attempts, such as the building of fish ladders, have been made in the past to reduce that impact. NRWA’s river continuity projects focus on examining existing man-made features that fragment our waterways, determining their current usefulness, and seeking methods to modify them that will allow our river ecosystems to return to a more natural state.


Hundreds of dams dot the landscape throughout the Nashua River watershed, remnants of industries long abandoned. A handful of the dams, mostly on the Nashua River Mainstem, include hydropower operations that actively generate power. Dams create small ponds and lakes, offering recreational opportunities and a link to a way of life from days gone by. An increasing number of dams, however, are falling into disrepair and are becoming a burden to dam owners liable for damages if the dams fail. Municipalities and private dam owners have to make the difficult decision regarding whether to repair, replace, or remove a dam. All three options are very costly, and the deliberations regarding the repair and continued upkeep, or removal of any dam involve ecological, safety, political, economic, and cultural issues.

NRWA’s policy regarding dam removal is to consider each on a case-by-case basis. Not every dam is destined to be removed. There are dams, however, that have reached their useful life, are expensive to rebuild, provide no ecological benefit, and in fact are a hindrance to the improvement in the overall stream ecology. Dams disrupt a river’s natural course and flow, raise water temperatures in the downstream reaches from the dam, and disrupt river continuity, resulting in isolating populations of fish and wildlife and their habitats within a river. Restoration of the natural flow to a river often results in the rebound in the diversity of aquatic life to a stream that supports the native species that depend on a free-flowing riverine system to survive.

Links to dam resources:
MA Office of Dam Safety
Division of Ecological Restoration
NH Dam Bureau


Culvert on brook in Fitchburg, MARiver and stream road crossings can be barriers to fish and wildlife movement if they are undersized, installed incorrectly, or are damaged from erosion and settling. Culverts can become “perched,” requiring fish to jump up into the culvert, which they often cannot or will not do. In addition, each year thousands of turtles and other wildlife are killed when they choose not to use an undersized culvert and instead attempt to cross a road.

NRWA hosted a stream continuity training session in the summer of 2009 organized by the Squann-a-Tissit chapter of Trout Unlimited and conducted by MA Riverways. Participants learned methods for conducting a stream continuity inventory. The goal of the continuity assessments was to identify crossings that are barriers to fish and wildlife passage and to help set priorities in restoring stream habitat in the Nissitissit and Squannacook watersheds. Project partners included NRWA, Friends of Willard Brook, O.A.R., the Pepperell and Townsend Conservation Commissions, MassWildlife, and the U.S. Geological Survey. More on the Massachusetts River and Stream Continuity Project.

In 2011, with generous support from the Stephen F. Quill Family Foundation, NRWA was able to take part in restoring connectivity along native reproducing brook trout habitat in Gulf Brook in Pepperell. The project was a partnership among the Massachusetts Outdoor Heritage Foundation, the Division of Fish & Wildlife, the Frank Nims Family Trust, the Greater Boston and Squann-a-tissit Chapters of Trout Unlimited, and the Town of Pepperell. The two new open (natural)-bottomed culverts replaced two old pipe culverts, which will allow brook trout the freedom of movement from the upper reaches of Gulf Brook to the Nissitissit River.

For more information on the NRWA’s river continuity projects, please contact Martha Morgan, NRWA Water Programs Director, at (978) 448-0299, or This email address is being protected from spambots. You need JavaScript enabled to view it..