In 2012 and 2013, Maine removed two hydroelectric dams from the Penobscot River; river herring later rose from almost zero to more than six million

A tiny fish is quietly telling one of the best environmental comeback stories in America, and almost no one outside New England has probably heard it. In 2012 and 2013, Maine lost two hydroelectric dams. According to a University of Maine research team writing in the journal Transactions of the American Fisheries Society, that decision triggered rapid, measurable changes across the entire fish community of the Penobscot River within just a few years after the dams were gone.

A river that almost went silent
200 years ago, industrial development forever changed the Penobscot. More than 100 dams were eventually built on the river, and pollution followed, according to NOAA Fisheries. The watershed once supported as many as 100,000 Atlantic salmon, tens of millions of river herring and several million American shad each year, NOAA Fisheries engineer Matthew Bernier told the agency.

By 2010, the collapse was nearly complete. That year, only two alewives, a type of river herring, were counted at the Veazie Dam, on a river that NOAA estimates once carried 14 to 20 million of them annually, in 2012, according to a report. For the Penobscot Nation, which has fished this river for thousands of years, that collapse was not only an ecological one. NOAA Fisheries says the tribe last harvested Atlantic salmon for ceremonial purposes in 1988 and that losing that fishing tradition has affected community health and identity ever since.

Two dams come down, and the water starts to breathe
According to Maine Boats, Homes & Harbors, crews removed the Great Works Dam in 2012 and the Veazie Dam in 2013. A third barrier, the Howland Dam, was not fully removed; instead, a fish bypass channel was constructed in the summer of 2016. Collectively, these projects reopened substantial lengths of river that had been blocked for about two centuries.

The results were soon in. NOAA Fisheries tracked the recovery over the same 20 years as its broader Penobscot restoration project, reporting an increase in river herring from virtually zero above the former Veazie Dam site to more than six million migrating through the restored river each year. The early trajectory was just as striking. By 2018, six years after the first dam was removed, Reasons to Be Cheerful reported that more than two million river herring were counted passing through a local fish lift.

Why a small silver fish matters this much
River herring may not be flashy, but they are a keystone species in the Gulf of Maine, according to NOAA Fisheries. From otters and osprey near the river to whales and cod far out in the Gulf, nearly everything in the food web eats them. Their return has also helped protect young Atlantic salmon as predators now have more to eat than just salmon smolts.

This pattern isn't unique to Maine, either. A 2023 study in the journal PLOS ONE found that river herring on Maryland’s Patapsco River also started recolonizing newly opened habitat within three years of the removal of another dam, suggesting the Penobscot’s quick rebound is part of a larger pattern that occurs wherever these barriers disappeared.

The salmon numbers are real, just smaller
Salmon recovery has been slower. According to NOAA Fisheries, the Maine Department of Marine Resources counted 1,520 Atlantic salmon on the Penobscot in 2023, the highest number in more than a decade and still well short of the watershed’s historic runs. Salmon need cold, densely forested headwater streams to spawn, and much of that habitat remains behind smaller dams further upriver, an ongoing restoration effort.

What this means for the rest of us
Even if you don't live by a river, you might find this encouraging. Dam removal is becoming quietly one of the more potent weapons in American conservation, and the Penobscot has become the case study everyone points to. The reopened river reaches saw a 31% increase in fish-community similarity scores after the dams came down, in large part because of anadromous fish like herring moving back in, according to the University of Maine research team.

For millennials and younger adults who are used to mostly bad environmental news, the Penobscot is a rare exception: a place where a handful of deliberate decisions led to a visible, countable outcome within a decade.