The Dammed: Getting Fish Back into American Rivers by Chipping Away at Dams

In another installment of the Tufts Environmental Studies Department’s Lunch & Learn Program, editor of Becky Kessler spoke about the history and effects of America’s many dams on fish populations. Kessler is a former senior editor at Natural History Magazine and her writing has appeared in the New York Times, Boston Globe Magazine, Yale Environment 360, ScienceInsider, and many others.

Dam with Fish Ladder- photo from

Dam with Fish Ladder- photo from

Early European and American explorers’ accounts of fish populations on the North American continent describe rivers so full of fish that it wasn’t clear if the river contained more water or more fish. Since then, America’s many species of diadronous migrating fish (atlantic salmon, american shad, alewife, sea lamprey, bass, sturgeon, and american eel) have drastically dropped in population. This is largely, though not entirely, due to the proliferation of dams.

The number of dams in U.S. rivers is unknown. Most counts depend on state inventories, which can have arbitrary height cutoffs and other reasons for leaving many dams out. One estimate, cited by Kessler, says there could be between 100,000 and 1 million. Dams result in a loss of river connectivity as fish are unable to swim upstream past even small sized structures. Some dams are equipped with fish ladders, which can be helpful but often only for particular species. Recent research has resulted in the development of “nature-like fishways”

Nature-Like Fishway-

Nature-Like Fishway

With increasing awareness of the unintended consequences of dams, many are starting to be removed. Around 850 have been removed in the last two decades. There is often opposition to dam removal as homes situated on a lake upstream from a dam would lose significant property value if they lost their waterfront character. The area behind dams tend to accumulate environmental pollutants, which would be stirred up and released all of a sudden if the dam were removed.

Bringing in the human element, Kessler discussed the irreversible effect that dams have had on indigenous peoples dependent on fishing for sustenance, both in the U.S. and abroad. The Belo Monte Dam on the Xingu River is likely to displace 20,000 mostly indigenous people. The Three Gorges Dam on the Yangtze River in China displaced 1.2 million people.

Next week’s Lunch & Learn will feature the Friedman School’s Timothy Griffin to talk about sustainable diets.