Fish Impacts

The Mascoma River provides important habitat for a variety of fish species, habitat that could be impacted by the introduction of a new dam on the river. The section of the river between the Mascoma Lake dam and Packard Hill Covered Bridge provides high-quality seasonal trout fishing, while the lowest mile was previously stocked with Atlantic Salmon as part of a conservation plan for reestablishing this species in the region (1). The figure below, taken from (1), lists the species of fish that are commonly found in the Mascoma River.

Craig Layne of the Dartmouth College Biology Department notes that the implementation of a dam would impact fish access to habitat and temperature. The dam would impede fish movement in the river, potentially a problem for native Brook Trout that spawn in the river; Atlantic Salmon have also been caught along the stretch of river leading to Mascoma Lake. It does not appear that there are any American eels in the river, though an updated survey may be necessary to make sure this is the case, but if they were present fish ladders would likely be required around the dam. A fish ladder could prove to be beneficial regardless for any species that may be traveling up the Mascoma River, and Tom Tarpy of Grafton Hydropower has stated that fish ladders would be implemented if it was found that migratory fish were using the river.

In terms of the creation of thermal pollution in the river, a lake-system environment would be created behind the dam, which would cause an increase in the temperature of the water here. Cold-water fish species, such as trout, would have difficulty surviving behind the dam, while warm-water species like small mouth bass and shiners would benefit. The dam would also impede fish movement to cooler water during the summer when the river heats up. This impact on fish species by temperature and the oscillation in water flow that a crest gate would produce would potentially upset and reshape the current trophic system in the river.

Additionally, water released when the pneumatic crest gate is lowered could carve into the downstream river channel, “causing channel incision and isolating it from adjacent floodplains or tributary outlets. Fine sediments are preferentially transported, often resulting in an excessive coarsening and armoring of the riverbed and a reduction in habitat quality for bottom-dwelling organisms” (2). The disruption in sediments and nutrients in the river would also negatively impact macroinvertebrates that fish feed on, thereby potentially impacting fish populations in the river. However, David Newlove notes that fish can sense an increase in water flow and swim up river to feed on macroinvertebrates and other organic matter being released by something like a crest gate, and warm-water species caught behind the dam and churned on the river bottom would provide important food for cold-water fish. David also stated that a dam that regulated water flow and ensured that there was a consistent flow of water downstream could also become beneficial to fish during the summer, when the river begins to dry.

All photos above taken by Kyle Kittelberger.