On a muggy day in late August, George Jackman, an aquatic ecologist who works on habitat restoration, stood at the edge of Quassaick Creek in upstate New York.
The Quassaick, which flows through the small city of Newburgh, New York, and spills into the Hudson River, was unusually shallow after a summer with little rain. “It looks bucolic now,” Jackman said. “But it can be a raging torrent.”
For 300 years, that torrent had been contained by a small dam that once powered a nearby mill, where the Stroock Felt company turned out carriage blankets for the horse-and-buggy trade, and later army blankets and woollen uniforms during the first world war.
Farther upstream, other dams once generated power to run local candle and iron factories, woollens and paper mills – sites that made Newburgh a bustling industrial town in the 19th and early 20th centuries.
Most of those factories have long since shut down, but their dams remained, and that has created an ecological problem that Jackman, who left his job as a New York City police lieutenant in 2005 to pursue a PhD in ecology, is determined to fix.
Tributaries like the Quassaick provide critical habitat for fish that swim upstream to spawn, such as river herring, striped bass and Atlantic sturgeon, and for species that do the reverse, such as American eels. Dams disrupt their ancient pathways, fragmenting habitat and interfering with the life cycles of these migrating species. Conservationists like Jackman, who works for the environmental group Riverkeeper, want to tear them down.
For him, the dams are an ugly reminder of a dreadful past. “This was a foul place,” says Jackman. When the dams powered nearby industries, he says, “there were no environmental laws. There were no child labor laws. There were no labor unions. There was no Clean Air Act, no Clean Water Act. This was a place of death.”
Jackman’s mission is to dismantle these “ghosts of capitalism”, as he calls the derelict structures, and bring the damaged ecosystems back to life.
He’s not alone: environmental movements in the US and Europe have been locking their sights on bringing down dams. In the Pacific north-west, Indigenous leaders have led the charge against the Gorge Dam, 100 miles north-east of Seattle. Last year, a record number of dams were removed from European rivers. And in New York state, activists’ demands are catching on, too. Two years ago, an excavator tore down the Stroock mill dam: a barrier that had blocked the path of migrating fish for centuries was gone in a week.
Riverkeeper wants to keep going, and is seeking funding to demolish the barriers upstream of the Stroock dam. “We are trying to return habitat to dispossessed organisms in long-term decline,” Jackman said.
It’s a matter of urgency, he said, not only because aquatic species are threatened but because the obsolete structures are failing. “If they were to breach in one big kinetic burst, some of these would endanger people’s lives.”
Before the dams were built, generations of river herring swam from the Atlantic Ocean into New York Harbor, up the Hudson River and into its many tributaries, following their instinct to search out cool stream beds where they could lay their eggs. But for the past three centuries, when the fish reached the Quassaick Creek, a journey of more than 50 miles from the harbor, they stopped short, blocked by the Stroock Felt mill dam and older dams before that. Their numbers began a steady decline.
Across America’s 3m miles of rivers, hundreds of thousands of dams built to power the factories of the early industrial era remain in place. In New York state, only half of the Hudson River’s 67 tributaries are free-flowing; the rest are blocked by as many as 2,000 low dams.
Dams fragment habitat, impeding the flow of sediment and nutrients, and degrading river ecosystems upstream and down. “With climate change, the waters are warming, so particularly for cold-water species, trapping them further downstream can be problematic for their survival rates,” said Serena McClain, the director of river restoration for the non-profit group American Rivers.
The dams are also a flood hazard: they were not built to withstand the stronger storms that have arrived with a hotter planet, and they are deteriorating. When they collapse, they can deluge bordering communities.
But these barriers are starting to come down. Since 1998 more than 1,500 dams have been removed across the country, according to American Rivers, including two large hydroelectric dams along the Elwha River in Washington state, which were imperiling wild salmon populations, and many more small ones such as the mill dams on the tributaries of the Hudson.
Some people have objected to dam removal projects on the ground that these remnants of America’s industrial heritage should be preserved. Others use the ponds the dams create for boating or swimming; property owners may fear draining the pond will leave an unsightly mud pit and ruin their waterfront view.
“Maybe they have a house, a dock, they fish there,” said Brian Rahm, the director of New York’s Water Resources Institute, which works on barrier removal. So Rahm works with landscape architects to sketch how the streams will look when the dams are removed and the shorelines restored and rewilded. “When they imagine change they can only see things going away; it’s hard to imagine the opportunity of what could be put there in its place.”
Farther upstream, Jackman hacked a path with a machete through a towering thicket of Japanese knotweed to reach the Walsh mill dam. The dam no longer powers the grist and sawmills that once stood nearby and is starting to crack, making it a hazard to its neighbors.
Just downstream is the Mullins Courtyard apartment complex, a housing development for low-income tenants that was built in the stream’s floodplain. The complex has been inundated during recent severe storms: after Hurricane Ida last September, the Mullins apartments flooded, and the playground was submerged under several feet of water. If the Walsh dam were to collapse in another hurricane the flooding could be calamitous.
To make matters worse, bordering the Quassaick is a sewer main – which if destroyed could inundate the area with human waste.
Such a flood could be financially devastating to the people of Newburgh, where more than twice as many people live below the poverty line as in the county at large. Low-income people are less likely to receive housing assistance from the Federal Emergency Management Agency after a natural disaster, and when they do receive funds, they tend to get less.
Riverkeeper has submitted a proposal to the National Oceanic and Atmospheric Administration for funding to continue their work on the Quassaick, hoping for a portion of the $800m set aside in last year’s infrastructure bill for dam removal. And across the Hudson Valley, more projects are planned as well; by 2030 the state department of environmental conservation’s estuary program intends to dismantle dams to reconnect at least 25 miles of streams.
Ecologists say that when even small and seemingly insignificant structures are taken down, there is a cascading effect on the whole riparian ecosystem. Sediment that once collected behind the barriers flows freely again, forming riffles, mudflats and sandbars that provide shelter for various aquatic creatures, and creating tidal marshes that help protect the shoreline from violent storms.
When the natural flow of a stream is restored, “you get a richer population of bugs, and the bugs feed the fish, and the fish feed the birds, and the birds provide a wider web of services, and other animals come in,” Rahm said. “You get a more resilient ecosystem all around, and it just ripples out from the stream.”
The evidence suggests that migrating fish find their way to their cool-water spawning grounds, even when their routes have been blocked for many generations. A study published in the journal BioScience found that “upstream migration was evident within weeks or months” after small dams were demolished in the midwestern and eastern US, and “up to 95% of all species found downstream of the dams migrated upstream within 1-3 years”.
In some cases, the fish move in much quicker: when a dam was removed from the Wynants Kill near Troy, at the upper end of the Hudson River estuary, within days underwater cameras recorded thousands of silvery river herring swimming into the newly opened stretch of river.
Before heading back to his truck, Jackman stood at the side of the Quassaick and pointed to where the creek had started to meander from its old course in the two years since the dam was removed. Now that the dam is gone, “the river is taking its form again,” he said. “We need to let the water go where it has to go.”