Since 2024 dam breach, free-flowing Nissequogue has begun to recover and habitat is improving
The Suffolk County Legislature has voted to issue a negative declaration for the proposed construction of a new dam at the former site of Stump Pond Dam in Smithtown, determining that the project would not result in significant adverse environmental impacts under the State Environmental Quality Review Act (SEQRA).
Save the Sound believes this decision fails to reflect the full scope of the project’s ecological and flooding risks.
Following the August 2024 catastrophic breach of Stump Pond Dam (also known as New Mill Dam) in Suffolk County’s Blydenburgh County Park, more than two miles of Long Island’s Nissequogue River returned to a free-flowing condition for the first time in roughly 200 years. Since then, the river has begun to recover. Native plants are reemerging from the seedbank across the newly exposed floodplain and wetland habitat, and bird diversity has increased, including 12 species reported at the park that had not previously been documented there. The river is already showing clear signs of ecological recovery and a return to more natural conditions.
By issuing a negative declaration, Suffolk County has chosen not to require a full Environmental Impact Statement before advancing a project that would reverse those gains and permanently alter one of Long Island’s most ecologically important rivers.
“This vote raises serious concerns,” said Sara Cernadas-Martín, PhD, director of New York Ecological Restoration programs at Save the Sound. “The Nissequogue is already recovering. Building a new dam would flood newly restored habitat, degrade water quality, interfere with aquatic connectivity, and diminish the floodplain’s ability to act as a natural reservoir that stores and slows floodwaters during storms. This is exactly the kind of project that warrants full environmental review.”
From an ecological perspective, keeping the river open is critical. A new dam would re-create an impoundment that warms the water, reduces dissolved oxygen, traps sediment and nutrients, and degrades habitat for fish and wildlife. These impacts are especially concerning in the Nissequogue, a rare cold-water river system that supports sensitive species, including native brook trout. The former pond had also suffered from cyanobacteria blooms and was overrun with invasive aquatic plants, conditions that a new dam could set in motion again. Since the breach, conditions in the river corridor have already shown signs of improvement, including cooler water temperatures, rapid vegetation recovery across the former impoundment, and increasing wildlife use.
The floodplain now emerging at Blydenburgh provides an important natural function of its own, acting as a natural reservoir for flood control by storing, spreading, and slowly releasing floodwaters. Reconstructing the dam would reduce that floodplain function and could increase upstream flooding during major storm events by backing water up into areas that are now better able to drain and absorb storm flows naturally. Multiple upstream homeowners have reported that since the dam breached, they have had less water in their basements and had to rely on their sump pumps less. Rebuilding the dam will raise the groundwater table again and bring those flooding and wastewater issues back. At a time of stronger and more frequent storms, this decision deserves careful consideration of how best to support long-term flood resilience.
Throughout the SEQRA review process, Suffolk County held multiple public hearings on the proposed dam reconstruction. Save the Sound scientists, engineers and attorneys provided public testimony at each, and together with the Free the Nissequogue Coalition, consistently urged the County to identify the project’s potential significant adverse environmental impacts in a positive declaration and prepare an Environmental Impact Statement. The New York State Department of Environmental Conservation also recommended a full Environmental Impact Statement and maintained that position in a follow-up letter to the County. DEC warned that the proposed dam construction appears to meet several indicators of significant adverse impact under SEQRA, including increased potential for erosion, flooding, drainage problems, destruction of vegetation and fauna, and interference with fish and wildlife movement. DEC also recommended that the County evaluate alternatives, including less impactful options, rather than moving directly to building a new dam.
Today’s vote is an important moment, but it is not the end of the process. The dam proposal must still move through additional permitting and regulatory review, where impacts on habitat, hydrology, water quality, and public safety will face further review. Save the Sound will continue working with Seatuck Environmental Association and the rest of the Free the Nissequogue Coalition, partner organizations, and community members to advocate for a science-based review and for a future in which the Nissequogue River remains free-flowing.
Enrico Nardone, executive director of the Seatuck Environmental Association, said, “While all of us involved in the Free the Nissequogue River Coalition are very disappointed in the decision of the Suffolk County Legislature, we are not giving up. We’ll continue to advocate for a free-flowing Nissequogue River, which we are confident is the right option for Suffolk County from a fiscal, climate resilience, and ecological perspective.”
This moment remains a once-in-a-generation chance to choose a healthier, more resilient river ecosystem. There are alternatives that would allow the Nissequogue to remain free-flowing while also supporting accessible recreation. As decisions about the river’s future move forward, we must ensure that the next generation can enjoy, learn from, and connect with a healthy river ecosystem.