Suffolk, state DEC at odds over county plan to rebuild dam at Blydenburgh Park in Smithtown

Suffolk and state officials are at odds over the county’s proposal to build a new dam at Blydenburgh Park in Smithtown, largely over the extent of the environmental review required.

The original Blydenburgh dam was built in 1798 to power a grist mill and remained, in altered form, until a severe rainstorm in August 2024 dropped 10 inches of rain across the North Shore. The heavy rain caused a partial collapse of the dam, which drained Stump Pond.

Since then, community opinion has been split between those who want to see a dam built and the pond re-created and those who say the Nissequogue River should be allowed to run free.

Suffolk County has proposed building a new dam, 500 feet wide and 10 to 17 feet tall, made of earth reinforced with a steel core. It would flood 118 acres of land to re-create Stump Pond, which also was called New Mill Pond and Blydenburgh Lake.

Park visitors were dismayed by the barren expanse of mud after the dam failed. The loss of the pond meant an end to many recreational activities, including fishing, boating and kayaking.

Opponents argue flooding the landscape would destroy the flourishing ecosystem that has established itself in the 17 months after the pond drained.

A Suffolk County panel is scheduled to vote later this month on whether to recommend a full environmental review of the dam project. The process could be lengthy. An environmental impact statement generally takes months to complete and can uncover reasons to disapprove a project.

The study would analyze the impact of a new dam on native species, flood mitigation and wetland habitats. The panel, which advises the Suffolk County Legislature, could also decide the project will have no adverse impact on the environment, which would fast-track a new dam.

A report from the Suffolk County Planning Department argued "the project will not result in significant adverse impacts." A dam would reduce the risk of downstream flooding and fish would be able to navigate past the barrier through a series of pools, the report said.

But Thomas Kohlmann, an analyst for the state Department of Environmental Conservation, suggested in a Jan. 3 letter to the county that it consider alternatives, including building a lower dam that would create a smaller pond and leave a large wetland area undisturbed, or simply leaving the river undammed.

Kohlmann advised the county that the dam could have a “significant adverse impact on the environment." That includes a greater risk of flooding and drainage problems, the destruction of many acres of plants, and harm to migratory fish and other wildlife, Kohlmann wrote.

He said the county should consider these and other consequences in a thorough environmental impact study.

DEC permits required

Even if the county declines to conduct the more extensive review, it will need to secure at least five permits from the DEC, and to prove its proposed dam accords with state laws on dam safety, preservation of wetlands and stream disturbance, among other regulations. Rules concerning “wild, scenic and recreational rivers,” for example, bar “any impoundment, diversion, or structures that impede or alter the natural flow of water,” Kohlmann said.

He added the county should consider potential damage to native plants and wildlife, noting that migrating fish often struggle to swim through human-built fish passages. The project could also threaten remaining stands of Atlantic white cedar, a threatened species in New York and a host plant for rare Hessel’s hairstreak butterflies, Kohlmann wrote.

A permit to alter a wetland can be issued only if there’s a “compelling economic or social need” that “substantially outweighs” the damage to that wetland, the DEC letter said.

Fiery meeting

A public meeting Wednesday of Suffolk's Council on Environmental Quality drew heated debate. The board is tasked with advising the legislature on the scope of the environmental review.

Suffolk Legis. Leslie Kennedy (R-Nesconset) called Blydenburgh Park “the jewel of the North Shore and our park system.” She said “for safety reasons, the dam must be rebuilt.”

Tom Norchi, who grew up visiting Blydenburgh Park swimming in its waters and whose children also walked in the park, said he was "gut-punched” by the draining of the pond. “It felt like a friend died.”

Some speakers described the ecosystem's transformation since the dam's collapse. By the middle of last summer, a riot of wildflowers and grasses erupted from the muddy pond floor, migratory fish once blocked by the dam started swimming to upstream spawning grounds, and wading birds such as herons and egrets took up residence.

Karen Blumer, president of the environmental nonprofit Open Space Council, said a dam could endanger native fish populations that have returned to the river since pond temperatures tend to be warmer than rivers. She asked for a full environmental impact statement.

Dara Illowsky, a staff attorney for Save the Sound, said there were “numerous significant environmental impacts” from the dam’s construction that warranted further analysis.

“A thorough examination of all reasonable options is essential to help identify the best solutions for community resilience, flood mitigation and ecological restoration,” she said.

The board will vote on its recommendation at a special meeting on Jan. 28 at the H. Lee Dennison Building in Hauppauge.