The presence of large sturgeon is just one indicator that the waterway is recovering from serious industrial pollution

New York’s Hudson river, once known as America’s Rhine in a nod to the famous European waterway, played a pivotal role in bolstering American power at the cost of decades of foul pollution.

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Last June, researchers were shocked to discover some startling evidence of the river’s belated recovery. Scientists searching for the endangered Atlantic sturgeon hauled a special sonar from the back of their boat, using sound waves to bounce down on to the riverbed and detect any creature swimming underneath. Incredibly, the outline of an enormous 14ft (4.3 metre) sturgeon appeared on the screen.

“I thought ‘this is a big one’ and when we got back I sent the image to some colleagues,” said John Madsen, a University of Delaware geologist who ran the research. “Typically we may see a fish as big as three metres, so to see something a metre longer than that is quite something. Everyone was surprised, they said: ‘wow you’ve got to be kidding me, that is crazy.’”

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The leviathan fish, most likely a female aged around 80 years old, is part of a population of about 450 adult Atlantic sturgeons in the prime spawning area of the Hudson, located near Hyde Park, Franklin Roosevelt’s former home, about 70 miles north of New York City.

This small population, Madsen said, suggests the rebound of a river that played a crucial role in the development of New York and, more broadly, the US. “I think it’s really encouraging. It’s a sign that the ecosystem and the fisheries are coming back,” he said. “It’s not like the problems have completely gone away, but the river is getting back into a better shape.”

Facebook Twitter Pinterest The presence of sturgeon in the Hudson river is a sign that the waterway is bouncing back from decades of pollution. Photograph: Jeb Wallace-Brodeur/AP

The Hudson, a 315-mile ribbon of water that rises in the Adirondack Mountains and empties in New York harbour, helped propel the economic fortunes of New York and the US as a key shipping route, particularly after the construction of the Erie canal in 1825 linked it to the Great Lakes.

Engineers deepened the river, speeding the way for larger ships but wiping out much of the shallow-water ecosystems that underpinned its beauty.

Almost as soon as the Hudson started to enrich the US the river spawned one of the first environmental movements in the country, as middle-class New Yorkers decried the logging of its surrounding forest and blasting of the Palisades, a line of steep cliffs on the west side of the river, for construction materials. The Hudson river school of landscape painting also sprang up, with artists’ work warning of the desecration of wilderness.

Pollution worsened after the second world war as heavy industry clustered around the Hudson. “I remember the river as polluted with sewage, butcher waste, industrial chemicals and heavy metals,” recalls Frances Dunwell, an author and coordinator of the Hudson river program at New York’s department of environmental conservation (DEC), in a new exhibition on the river in New York City.

“People swam in the river, but at their own risk. People fished in the Hudson, but the fish tasted like oil.”

Oil, heavy metals, dye, solvents, cleaning fluids and paint were all dumped into the Hudson by factories turning out cars and paper. Stretches of the river were essentially dead, with the fish deprived of oxygen in the water. “Back in the 1970s, fishermen in the lower river could tell what colour General Motors was painting cars that day by looking at their nets,” said John Cronin, a fisherman turned conservationist and academic who has worked on the Hudson for the past four decades.

Facebook Twitter Pinterest The Popolopen creek feeds into the Hudson river at Bear Mountain, 50 miles north of New York City. Photograph: Alamy Stock Photo

The recovery of the Hudson has gathered momentum since local environmental activism helped inspire intervention by the courts and then the federal government to tackle the pollution. The Clean Water Act has curbed the practice of haphazardly dumping toxins into the river and the decline of industry in the region has removed many of the most obvious blights.

Some problems linger. Power plants, such as the Indian Point nuclear facility, draw in cooling water from the Hudson killing millions of fish a year. “They are essentially giant mechanized fishermen,” Cronin said. Meanwhile, the Environmental Protection Agency deems 200 miles of the Hudson a toxic Superfund site because of contamination by polychlorinated biphenyls, or PCBs.

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General Electric spent five years dredging the riverbed to clean up the PCB problem, although it has not proved a panacea. “The levels of contamination of both fish and sediment have remained troublingly high,” admitted Basil Seggos, head of the New York DEC, in January.

Still, swimming and kayaking now occur safely and regularly on the Hudson, a marked improvement from just a few decades ago and the survival of the sturgeons suggests it can morph back into a fully functioning ecosystem. The largest looming threat may lie many miles south in Washington DC – the Trump administration has vowed to scale back the scope of the Clean Water Act and loosen rules on toxins dumped into waterways by power plants.

“There’s no question that the Hudson is a cleaner river. There is a lot less pollution now,” Cronin said. “It’s an environmental success story but it’s an incomplete job, the work isn’t over. It’s not enough to reduce pollution: you need to restore the ecosystem. You may be able to swim in it but does it have frogs and turtles and fish?

“The goals of the Clean Water Act are overdue by decades. Right now we need more aggressive and ambitious laws and there is an administration and Congress in DC interested in weaker laws.”