On the broad, flat flood plainwhere Blydenburgh Park's Stump Pond used to be, wild grasses have sprouted from the long-submerged seedbed and clusters of forget-me-nots, irises and buttercups have sprung from the muddy bottom.

From a wooden pier that served as a boat launch before the pond drained last summer, birdsong seemed to come from all directions on a sunny May morning: red-winged blackbird, Carolina wren, spotted sandpiper, red-eyed vireo, catbird, Northern mockingbird, great crested flycatcher and a chimney swift were all calling, according to Merlin, a birding app.

And a little farther in the distance, a swift-moving stream was finding its meandering path through the altered landscape.

"The river is behaving naturally now," said Andrew Fisk, Northeast regional director at the nonprofit American Rivers, "setting out a channel as it heads to Long Island Sound."

The dam in Blydenburgh County Park in Smithtown collapsed in Augustafter a torrential downpour dropped more than 10 inches of rain. Millions of gallons of water rushed past the broken dam and into Long Island Sound.

Visitors to the park after the storm were shocked by the sight: the barren pond floor studded with the stumps of trees felled 200 years ago before the area was flooded. Nine months later, parts of the flood plain, especially near the dam where the sediment is thickest, are still mostly bare, with just a few grasses emerging as the silt dries out and the weather warms.

The collapse touched off a debate that speaks to the question of how to manage Long Island's natural places: should the pond be recreated for human use and enjoyment, or should the Nissequogue River be allowed to run wild?

Suffolk County officials, fishermen and many who have enjoyed the pond over the years are keen to have the dam rebuilt and the pond returned, largely as it existed for two centuries. 

Stump Pond — also known as Blydenburgh Lake and New Mill Pond — was "a great recreational facility," County Executive Edward P. Romaine said in an interview. "If we don’t rebuild, it could go into a marshland and meadowland. ... A pond will get more use."

But ecologists, trout fishing enthusiasts, birders and others are hoping the Nissequogue will be allowed to remain in its natural state, flowing freely through this nearly mile-long stretch of its course, as it did for thousands of years before the dam was built.

"A river wants to be a river," Fisk saidin an interview. "And removing a dam is the quickest, most effective way to make a river healthy."

Across the country, more than half a million dams block America’s rivers and streams, most of them small dams that once powered grist, textile or sawmills in the early years of the industrial revolution. Most were abandoned as new technologies made them obsolete. Many fell into disrepair; others, like the Blydenburgh dam, originally built in 1798 for a grist mill, were reconstructed to contain ponds used for boating and fishing.

Over the years, scientists have documented how these hundreds of thousands of dams have damaged the country’s rivers and estuaries — preventing migrating fish from reaching their spawning grounds and sending populations into decline, starving coastal wetlands of nutrients and sediment, and thinning native species that can’t thrive in warm, still water while allowing a less diverse array of invasive species to take their places.

In the past 25 years, a movement to remove dams has spread from coast to coast, but has bypassed Long Island. Since 1999, more than 2,000 have been dismantled across the country, Fisk told Newsday; last year alone, according to American Rivers’ inventory, 108 barriers in 24 states were taken down, rejoining 2,528 miles of disconnected river habitat. The group is hoping to step up the pace, with a goal of working with local partners to remove a thousand dams a year — a total of 30,000 by 2050.

All but a very few of Long Island’s approximately 140 rivers and streams have been dammed, often with multiple barriers, fragmenting the waterways and degrading habitat. According to a state inventory, 96 dams remain in Nassau and Suffolk counties,but Enrico Nardone, director of the Islip-based Seatuck Environmental Association, says this is a significant undercount. 

In the past 20 years, six Long Island dams have collapsed and have not been rebuilt, including Blydenburgh and Stony Brook, which failed in the same August storm. (Stony Brook's mill pond was in a more populated area and has not been the subject of the same campaign.) But according to Nardone, "there has never been an intentional dam removal" on Long Island.

He and a growing coalition of conservationists are suggesting the Nissequogue could join this slowly expanding network of free-flowing rivers. Seatuck and Save the Sound are leading the campaign, joined by local, regional and national organizations including Defend H20 in Sag Harbor, Trout Unlimited, American Rivers, The Long Island Conservancy, Open Space Institute, Native Fish Coalition and Four Harbors Audubon Society.

The Nissequogue "really represents kind of a North Star of river restoration on Long Island," said Jake Dittes, Save the Sound’s director of Connecticut ecological restoration programs.

Ever since Stump Pond emptied, county officials have been calling for a new dam and new pond. When the dam failed, Romaine told Newsday last month, a lot of habitat was lost for lake fish and ducks. Without a dam, the landscape "will be something like a mud pit — not something that someone can enjoy," he said. "We are rebuilding this dam," he insisted.

The Suffolk County Legislature appropriated $6.6 million for the project in December, though the county’s chief engineer, Alex Prego, acknowledged at a recent public meeting in Smithtown the actual cost could be higher.

The first $600,000 is funding a study of the river’s 40-square-mile watershed, which will consider historical weather data to inform the design of a new dam, Prego said.

Romaine said in a press statement last month he had asked the public works department to "move as quickly as possible" to "begin the process of bringing [the] pond back to the community."

Many in the community are eager for that to happen. Jim Jonke, president of Long Island Bassmasters and the founder of the Stump Pond Restoration Coalition, said the pond has been a popular spot for fishing for largemouth bass, perch and sunfish, but the space is now a dangerous mudflat, infested with mosquitoes. With the dam gone, he said, "the property is unusable. There’s nothing to do there."

David Reisfield, president of the Long Island Greenbelt Trail Conference, said hikers enjoyed the expansive views across the water from the trail that circled Stump Pond and lamented that as the vegetation fills in, they won’t be able to see the more distant water. "It'll be a lot less nice to look at," he said.

Conservationists argue that even without a pond, there will still be plenty to do. The millions of dollars it would cost to build and maintain a dam and its impoundment could be used to renovate the neglected Blydenburgh mill, build boardwalks and viewing platforms into the wetland and along the water, and bridges that could provide views up and down the river. 

They say there's no doubt that a free-flowing Nissequogue is far better for the ecology of the river and its estuary. The lessons of previous dam collapses and removals is that nature knows how to restore itself. Just a few months after a dam collapsed at West Brook in Islip, the muddy stream banks were adorned in a riot of wildflowers, cattails and shrubs.

When dams come down, "you see things come back very, very quickly," Fisk said. Within a season or two, the former contours of Stump Pond will be cloaked by a lush riparian meadow, he predicted.

If the Nissequogue is un-dammed, migrating fish such as American eel and alewives, a type of river herring, will surge upstream in search of mates and a suitable place to lay their eggs. Populations of these fish, which spend part of their lives in freshwater and part in the ocean, are falling precipitously across Long Island, "primarily because their spawning habitat has been so greatly diminished with all the dams and culverts," said Dittes, of Save the Sound.

Brook trout — the only trout native to Long Island — might also repopulate the Nissequogue. The river would once have supported these fish, which need cold, fast-running streams, said Rick Vickers, president of Long Island Trout Unlimited. But "trout were no longer in the pond because they can't survive at those temperatures." 

"It's really in the service of the health of the entire environment to have a free-running stream," Vickers said. 

Though Prego said the county would build a fish ladder alongside a new dam to assist migrating fish, experts say recent studies have found an artificial ladder is a poor substitute for a river without barriers. John Turner, a conservation advocate at Seatuck, said up to 70% of fish will manage to navigate some fish passages; at others, a mere 5% to 15% will find their way.

"You're always taking a chance with a fish ladder that it's not going to work well," said John Waldman, an aquatic biologist at Queens College who studies fish migration.

It’s not just the river-dwelling species that will benefit, conservationists argue. For centuries, the nutrients and sediments that should naturally flow downstream and into the Sound have been halted by the dam, sinking to the pond floor. Now that those sediments are flowing again, they will enrich the coastal wetlands, which need sediment deposits more than ever to keep up with rising seas.

There’s also a public safety argument for taking out the Blydenburgh dam: A natural flood plain typically reduces flooding upstream and down, according to FEMA, by spreading out and storing stormwater. When a torrential downpour falls on an already-filled pond, it has no place to go — and that can lead to dam failure.

If the Blydenburgh dam is not rebuilt, there will still be two more dams on two different branches of the Nissequogue, at Millers and Phillips ponds. Ecologists have been talking for several years about removing the Phillips dam in particular, Nardone said, which would open up the last three-plus-mile stretch of the river as it winds north to Smithtown Bay. "I'm optimistic that we're going to be able to take that dam out one of these days," he said.

Prego, the engineer, said at the public meeting the county hopes to begin construction on a dam next year.

But the project will have to be reviewed by the Suffolk County Council on Environmental Quality, which advises the legislature on whether a full environmental impact study should be done. The county will alsohave to apply for permits from the state Department of Environmental Conservation and from the U.S. Army Corps of Engineers, which oversees construction in and around federally protected wetlands and waterways.

It’s rarely a speedy process.

In the meantime, native species are already finding their way to the river. Just recently, Nardone said he saw a solitary sandpiper foraging by the water — "a bird you would never see at the pond." By the time any construction on a dam could begin, the former pond basin will have become a flourishing wetland meadow, Nardone said. As the debate continues, the Nissequogue continues to flow, carving out its newfound path to the Sound.