What happens when you remove a dam? One year later, life returns to a Hudson River tributary

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Riverkeeper & volunteers planted 60 trees & shrubs this month along Furnace Brook, aka Jamawissa Creek, in Westchester’s Oscawana Park. The once-stagnant stream is coming back to life with mussels, fish – and a few surprises.

One year after a 5-foot fieldstone dam came down on Furnace Brook in Westchester, once-stagnant waters are flowing with new life. Mussel shells are scattered on the banks, presumably left by raccoons feeding on them. Creek chubs, white suckers, brown trout and other fish are finding their way through, where they were once blocked.

River herring and eels, migrating up from the Hudson River Estuary, can now move further upstream without hindrance.

We’ve also seen blue crabs. “It’s really a lovely surprise,” Riverkeeper’s George Jackman says. “They’ve become an integral part of the food chain. We may have forgotten that crabs use our freshwater creeks, but these are a migratory species, as much as a river herring or an eel.”

The stream itself is moving too, forming a sediment bank where the dam used to be and making a peninsula around a sapling that had stood by itself on an island below the dam.

“This was all a backwater eddy,” Jackman says. “The stream has a choice, where it never had a choice before.”

After allowing a year for the stream to re-establish its path, Riverkeeper returned on October 8 to plant trees and shrubs that will help stabilize the new bank, prevent erosion and create shade that helps cool the water so that fish can thrive. The plantings will also help repair a slope where the dam removal machinery came through. Behind the sapling, an American elm, we planted other yearling trees.

Riverkeeper staff members, along with volunteers from Waterkeeper, the Student Conservation Association and the community, planted 15 trees and 45 shrubs provided by the state Department of Environmental Conservation’s Trees for Tribs program.

This is an ongoing effort with DEC and local communities to restore streams that were stifled by human alteration, and return ancestral habitat to migratory fish. In July, we teamed up with Quassaick Creek Alliance and planted 50 trees at the site of a dam removal in Newburgh.

Furnace Brook was known to Native Americans who lived in the area as the Jamawissa Creek, meaning “Place of Small Beaver” – which it is. In 2018, a fish sampling survey found a surprising diversity of fish just below the dam. Here in Westchester County’s Oscawana Park, the stream has begun to recover its natural state, with the removal of debris, an old bridge, and the dam. Further upstream, a much larger dam – 25 feet high and 160 feet across – is slated for removal next.

Dams block migratory species, like river herring, that rely on tributaries like these as critical spawning grounds. About 1,700 dams – potentially 2,000 or more – fragment the rivers and streams of the Hudson Valley. Most are obsolete and many are hidden from view. The removal of these dams helps restore habitat here in the Hudson at a time when freshwater life is imperiled worldwide.

Learn more about dam removal at Riverkeeper.org/dams, and sign up to receive updates.

View a film clip by Jon Bowermaster with Jackman, Riverkeeper’s Senior Habitat Restoration Manager, discussing “Habitat Restoration” at Furnace Brook with Patrol Boat Captain John Lipscomb, and see more photos below.