Essex 19 Dam

The Winooski River pours over the Essex 19 dam in Vermont.

Dams have some of the greatest impacts of any human modifications of the landscape. A strategically placed dam can flood a river valley for many miles, creating a reservoir that covers hundreds of square miles of land area. This kind of river management can offer tremendous benefits, but dams also have notable adverse effects on water quality and habitat.

The physical, chemical, and biological impacts of dams alter river function and ecosystems. Dams can change in-stream water temperature and the amount of oxygen available in the water for fish and other aquatic organisms. Water impounded by dams is often warmed and is not suitable for cold-water fish species when released downstream. Dams disrupt the natural delivery of sediment, large woody debris and other organic matter to downstream portions of the river. These materials are a normal part of a river’s state, helping the regular regeneration of habitat, providing nutrients, and serving as shade and shelter for life in the river.

Perhaps the most significant impact of dams is their role as barriers to spawning fish and the passage of other aquatic organisms. These structures have cut off many miles of streams and rivers. As a result, populations of many native fish, including landlocked Atlantic salmon and brook trout, have declined drastically in the last century. In an effort to circumvent these barriers, fishery managers have installed fish lifts and ladders at some dams to help the passage of these and other species.

Recently, the benefits of dam removal have been increasingly recognized not only by anglers, scientists and river managers, but also among local officials, tourism boards, and the general public. In 2015, the Willsboro Dam on the Boquet River in New York was demolished after a community effort to bring the river and its fish population back to its pre-dam condition. In Vermont, a dam task force has been established to evaluate and prioritize dams for removal, particularly those that no longer serve a useful purpose.

In many cases, dams still serve an important function or are part of a community’s identity. The effort to balance improvements to river ecosystems with the social and economic benefits provided by dams will help to characterize the region’s prioritization of a high quality of life that allows for and benefits from a healthy environment.


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