Let the Nissequogue Run
The Nissequogue River is the longest river on the North Shore and the largest, by volume, on Long Island. Its size, the amount of water it discharges and the extent of its watershed are all a product of the river’s unique geological history – and make it the most ecologically significant river on the North Shore.
The river primarily exists between the Ronkomkoma and Harbor Hill Moraines. Several branches converge from the slopes of the glacial moraines, then flow north, through the Harbor Hill Moraine, into Long Island Sound.
The river’s two largest branches originate in forested wetlands in Hauppauge and meet in Blydenburgh County Park, where the river was dammed two hundred years ago to form Stump Pond for the purposes of powering a mill. The dam that formed the pond failed during a storm in August 2024.
Don’t Rebuild the Stump Pond Dam
The argument for allowing the Nissequogue River to run free through Blydenburgh.
In August 2024, when catastrophic rains caused the Stump Pond Dam on the Nissequogue to fail and the pond in Blydenburgh County Park to drain, it was understandable there was an immediate call to repair the dam; the lost pond was valued community resource that had been part of the landscape for hundreds of years.
But there are strong fiscal, resilience and ecological reasons for not rebuilding the dam and instead allowing the Nissequogue River to revert to its natural free-flowing state. As outlined below, when all factors are weighed over the long-term, the broader public interest is served by letting the river run free.
Fiscal Impacts
The costs of rebuilding the dam will be significant, likely exceeding $10 million, and maintaining it will add millions more in costs over the dam’s lifetime. Further, dealing with the inevitable issue of submerged aquatic vegetation in the pond will be a never-ending problem and an additional drain on county resources. Allowing the river to run free will cost the county nothing, except the cost of constructing a bridge to reconnect the Long Island Greenbelt Trail. Click here to read more.
Resiliency
Rivers are most resilient when they’re allowed to flow naturally through a healthy floodplain. A free-flowing Nissequogue River – which includes the waterway itself, as well as its associated wetlands and floodplains – provides natural infrastructure that delivers cost-effective resiliency services by capturing, slowing and modulating stormwater and carrying it safely to the sea. Click to read more.
Ecological Health
A free-flowing Nissequogue River is, in every way, ecologically healthier and better for more species of native wildlife than a river that is impounded by a dam. From habitat for native fish and birds, to improved water quality, to the transport of sediments and nutrients, a flowing river provides a wide range of ecological benefits. Click to learn more.
Fish Passage
If the dam is rebuilt, even with a fish passage solution in place, it will still impede the transport of sediment and nutrients, create a thermal barrier to fish migration, produce conditions favorable to non-native species and generally degrade habitat (both upstream and downstream). Even the best fish passes fail to move all fish and to address the ecological problems caused by dams and impoundments. Click to learn more.
Recreation
Blydenburgh County Park can continue to provide robust public recreational opportunities without Stump Pond. A bridge can replace the dam to reconnect the Greenbelt Trail; the cold-water river can provide opportunities to catch native brook trout; diverse riparian habitat can expand chances to view wildlife; and new bridges over the river’s branches can expand hiking options. Click to read more.
History
The site’s significance as an important part of Long Island’s colonial history is not lost with the river reverting to its natural state. The mill house still stands and – at a fraction of the cost of rebuilding the dam – could be renovated to significantly expand interpretive education about the site’s rich history. In addition, a free-flowing Nissequogue more accurately reflects the historical role the river played for thousands of years for Long Island’s native inhabitants. Click to read more.
How Removing Dams Benefits People & Rivers
This short video from American Rivers explains the benefits of allowing rivers and streams to run naturally.
Fiscal Impacts
The costs of rebuilding and maintaining the Stump Pond Dam will be significant. Rebuilding the dam is already estimated at over $6.5 million and is likely to be higher, especially if a fish passage structure and emergency spillway are included. And the long-term costs of maintaining the dam throughout its lifetime and keeping it in compliance with New York dam safety regulations will also be onerous, especially if the dam is reclassified, as expected, to the Intermediate Hazard (class B) category.
In addition to these substantial public expenditures, the county will also be burdened with maintaining the pond itself. As the dam slows the flow of water, the river will naturally drop its sediment load, creating inherent maintenance problems as the natural sedimentation process inevitably reduces the pond depth. This will eventually make it more difficult to enjoy the pond by boat and create conditions that are more suitable for “submerged aquatic vegetation” (SAV), especially in the pond’s warm, stagnant water. Problematic SAVs come in the form of both invasive non-native species, such as water chestnut and native species, such as yellow pond lily.
As SAVs take hold – as they did in Stump Pond prior to the dam failure – they’ll make boating and fishing more difficult and degrade the overall ecological health of the waterway. This is especially true if some of the most worrisome invasive species return and take hold, which is likely as some, such as hydrilla and Eurasion watermilfoil, have been repeatedly documented in Stump Pond over the past two decades.
There is no easy or inexpensive solution to dealing with the related problems of sedimentation and aquatic vegetation. They require either dredging to increase the depth of the pond or removal of the plants through mechanical harvest, hand-pulling or the application of herbicides. And, importantly, even after harvesting or treatment, SAVs are almost certain to return as long as the favorable conditions persist. It is hard to overstate the challenge that SAVs present to municipalities; even the best options are expensive and temporary. The extent of the problem is evidenced by the fact that many of the worst SAV problems have gone unaddressed in impoundments across Long Island. Some ponds have such an extensive problem that they are completely covered by plant growth in the summer. See, for example, the photo to the right of a pond dominated by yellow pond lily.
Of course, the best solution to addressing SAVs is eliminating the conditions that allow them to thrive; that is, by removing dams, dewatering the warm-water impoundments where they dominate and restoring cold-water, flowing streams, which are rarely dominated by aquatic vegetation.
While invasive plants would be a threat to the banks and floodplain of a free-flowing Nissequogue River, such outbreaks would be easier to identify and address because they’ll be on dry land. Species such as phragmites and knotweed can be managed by herbicides, mechanical removal and/or hand-pulling. This is especially true if outbreaks are identified and addressed before dense stands take hold.
Seatuck has demonstrated the potential of volunteer-based hand-pulling of phragmites at West Brook in Bayard Cutting State Park, where an ongoing effort has kept the invasive plant from overtaking the site of a former pond basin after a 2019 dam failure. And at West Brook the challenge was significant because there was a large existing stand of phragmites around the edge of the former pond. At Blydenburgh, on the other hand, there are only small pockets of phragmites that could be easily addressed before the invasive became a major problem.
In addition to SAVs, artificial ponds also create ideal conditions for harmful algal blooms (HABs) and blooms of dangerous cyanobacteria (a.k.a., blue-green algae). The organisms that cause these blooms naturally occur in fresh water, but they become dangerous to people and pets when they thrive in the right conditions and reach high densities. The ideal conditions for HABs are generally found in shallow, warm, nutrient-rich lakes and ponds – exactly the conditions created by dams. Conversely, cool, naturally flowing streams are not as susceptible to conditions that lead to the proliferations of HABs.
Resiliency
Generally speaking, when ecological features of the landscape – from forests to rivers to shorelines – are healthy, they’re more able to adapt naturally to changing conditions and to support resilient landscapes and communities. This includes contending with the intense rain storms and other challenges that a changing climate is already bringing to Long Island. Put simply, naturally flowing rivers and streams are more resilient than those that are artificially impounded and constrained.
A healthy, free-flowing Nissequogue River – which includes the waterway itself, as well as its associated wetlands and floodplains – would provide natural infrastructure that delivers cost-effective resiliency services by capturing, retaining, and filtering stormwater and modulating floods. The wetlands and floodplain of the river would act as natural sponges to soak up stormwater (and storm surges within the tidal zone). But this natural carrying capacity is lost if these features are already filled with water by an artificial pond or lake. An analogy is a bucket put under a sink to catch water in case of a leak – it’s going to be a lot more useful if it’s empty than rather than already full of water.
In addition, dams, by their very nature, create resiliency risks by impounding millions of gallons of water upstream from homes, businesses and public infrastructure. This risk of dam failure and the high cost of guarding against it is a major reason (or in many cases, the major reason) that dams have been coming down across the country. Long Island’s small, low-head dams generally don’t rise to the level of being considered “high-hazard,” but the experience of last year should begin to change the way we think about the risk.
It has been suggested that rebuilding the Stump Pond Dam will alleviate the flooding of nearby homes and businesses that has reportedly occurred since the dam failure. While we don’t have reason to doubt that people experienced flooding in the wake of the August storm, we are certain any current flooding is not related to the absence of the dam itself. In fact, with the dam gone, it is less likely that neighbors, both downstream and in the vicinity of Blydenburgh Park, will experience flooding related to the Nissequogue River. With its natural floodplain restored, the river will have room to expand during storm events and to attenuate potential flooding impacts.
Ecological Health
Resident Aquatic Wildlife
Prior to the construction of Stump Pond Dam (and the downstream dams), the Nissequogue River was a groundwater-fed, cold-water coastal stream, primarily flowing under the canopy of dense forest. It provided habitat for a range of fish and other resident wildlife adapted to flowing, cold-water conditions, including Brook Trout, New York’s only native trout.
When the river was dammed to form Stump Pond, more than a mile and a half of river (a long stretch of river by Long Island standards) was flooded and replaced by impounded, slow-moving, shallow water, which was warmed significantly by the sunlight reaching through the cleared forests. The substantially different habitat was eventually occupied (both naturally and artificially) by species suited to the new, unnatural conditions. Whether native to upstate New York (e.g., Largemouth Bass) or non-native (e.g., Common Carp, Red-eared Slider, Mute Swan), these new residents were never part of the river’s native wildlife assemblage.
Brook Trout are Long Island’s only native trout species; they’re a vital part of river ecology and an iconic coldwater sportfish.
Want more? Click for 10 mins of beautiful brook trout footage!
Diadromous Fish
Coastal rivers and streams play an important role in connecting upland habitats to the sea; they are avenues for the movement of nutrients, sediment and wildlife. A key part of this connection are the unique fish, known as diadromous fish, that split their life cycles between fresh and salt water. Long Island’s rivers and streams were never large enough to support salmon (the most well-known diadromous fish), but most, including the Nissequogue, did host annual migrations of alewife, blueback herring, American eel, rainbow smelt, and sea lamprey.
Other local diadromus fish, such as striped bass, American shad and white perch, used the lower portions of the river, even if they didn’t spawn in the river. Importantly, before being dammed, the Nissequogue (like other Long Island rivers and streams) also hosted populations of “sea run” or “salter” Brook Trout. These fish, considered semi-diadromous, spawned and primarily lived in freshwater, but moved into the estuary to feed throughout the course of the year.
Alewife spawning in headwaters of Sunken Meadow Creek after migrating from the ocean.
Critically, through their remarkable life cycles, these fish deliver ocean-derived energy and biomass into the waterway and provide important forage for a wide range of species throughout the estuary, from whales and striped bass to osprey and river otters. In this sense they play a vital role in driving our entire coastal ecosystem. Dams like the Stump Pond Dam block the access to freshwater habitat that these fish require, which has helped to drive significant declines in their populations.
Riparian Habitat
While the failed Stump Pond Dam initially left a muddy mess, it won’t last for long. With the arrival of spring in a few weeks, as the pond basin continues to dry and the soils warm, a natural restoration process will commence. Native plants will grow from the seedbank and rapidly form a riparian meadow that buzzes with the activity of insects and birds. Like everywhere, invasive species may have to be managed, but if left alone such sites eventually succeed into native riparian forests.
New York State Parks has experienced this natural restoration process at several locations on Long Island, including most recently at West Brook in Bayard Cutting Arboretum. After a dam failure in 2019, the muddy mess of the former pond quickly dried out and turned into a meadow of native plants (see images at right). In the years since it has matured and diversified, with shrubs and trees already taking hold.
At Blydenburgh, the Stump Pond site will likely eventually be repopulated and dominated by Atlantic white cedar. This conifer, which grows over 100 feet tall, historically occurred throughout the Atlantic coastal plain. Most New York occurrences were on Long Island, where it grew in dense stands along streams and rivers. The tree was heavily timbered for its light, durable wood, which was used for everything from shingles to fences to water pipes, and which lead to it being was heavily timbered during the colonial era. Harvesting and the development of riparian areas have led to the tree’s significant decline; it is listed in NYSDEC’s New York State Wildlife Action Plan as a “Proposed Plant Species of Greatest Conservation Need.”
However, remnant populations can still be found across Long Island, including a stand of over 100 trees along the southwest branch of the Nissequogue River in Blydenburgh Park – it is one of the largest remaining populations on Long Island. Given the tree’s high rot-resistance, the stumps that gave Stump Pond its name are almost certainly Atlantic white cedar. The potential to allow the existing Blydenburgh stand to expand and reclaim its former habitat is along the Nisseqougue represents a rare opportunity to reconnect to Long Island’s ecological heritage.
The riparian habitat at the Stump Pond site, as it undergoes a natural restoration and successional transition from meadow to shrub to forest, will provide important wildlife habitat, fight climate change by sequestering carbon and increase resiliency by attenuating storms, buffering winds and holding on to soils. In addition, as discussed below, the process will also increase the amount of open space available to the public for hiking, wildlife viewing and nature enjoyment.The riparian habitat at the Stump Pond site, as it undergoes a natural restoration and successional transition from meadow to shrub to forest, will provide important wildlife habitat, fight climate change by sequestering carbon and increase resiliency by attenuating storms, buffering winds and holding on to soils. In addition, as discussed below, the process will also increase the amount of open space available to the public for hiking, wildlife viewing and nature enjoyment.
Water Quality
Dams not only create poor water conditions in the impoundments they create, but also degrade downstream water quality by increasing average overall temperature and increasing levels of dissolved oxygen. The impoundments created by dams have a much larger surface area than the preexisting river, which results in considerably more solar warming. Numerous studies have documented that water temperatures downstream of dams can be, on average, several degrees (F) higher than temperatures upstream of the impoundment, with differences as high as ten degrees.
Indeed, the Long Island Trout Unlimited chapter found similar results on Long Island. A five-year effort to collect temperature data from the Carlls River in Babylon confirmed these staggering impacts. The data showed temperatures at the outflow of Southard’s Pond consistently more than five degrees warmer than water above the impoundment from May through September, and often approaching ten degrees warmer (see chart at right).
Increases in water temperature can impact cold-water species, such as brook trout, and favor non-native warm-water species, which can shift overall community composition and reduce ecological health. In addition to temperature impacts, dams can also reduce levels of dissolved oxygen in downstream waters, by slowing water, reducing atmospheric mixing and increasing decomposition. The unavailability of sufficient oxygen can reduce the success of a range of aquatic species.
Sediment Transport
Rivers not only move water, but they also carry nutrients, sediment and debris downstream. As discussed above, dams interrupt this important natural process, which results in an accumulation of sediment behind the dam and the related problems of submerged aquatic vegetation and poor water quality. However, dams also degrade downstream river habitat, leaving it “sediment starved” which leads to higher rates of erosion, reduction in riparian plants, and increased scour of the stream bed. Dams also starve the lower river of logs and other large debris which plays a role in creating pools and adding complexity to the habitat.
The failure or removal of dams reestablishes connectivity of sediment and nutrient flow between the upstream and downstream sections of the former dam site, creating new aquatic and terrestrial habitat to be colonized by invertebrates, vegetation, and fish. Without dams, there is less habitat fragmentation, more floodplain connectivity and restored natural flow patterns. These changes in sediment transport and habitat connectivity increase macro invertebrate abundance in downstream areas and reduce differences in species assemblage in areas previously separated by the dam.
Birds
One concern that has been raised since the dam failure is the loss of open water habitat for birds. Many of the species that used the pond, such as Belted Kingfisher, Great Blue Heron, Osprey and Mallards, will continue to use the flowing waterway. While the loss of open water will reduce habitat for some resident species, such as Mute Swans, and several species of migratory waterfowl that overwinter on Long Island, the habitat provided by Stump Pond was not unique in region. Waterfowl will easily find other suitable habitat in nearby lakes, ponds and bays, including at nearby Lake Ronkonkoma, a natural lake that hosts a significant gathering of waterfowl each winter.
However, the loss of habitat for some species at Blydenburgh will be more than offset by the gain for others. The diversification of the riparian area, to include meadows, shrubs and other habitat types will benefit and provide nesting and foraging opportunities for a greater diversity of bird species. In fact, the expansion of wildlife using the former Stump Pond site has already begun, even without a full growing season. Since the dam failure there have been six bird species documented for the first time at Blydenburgh County Park. These species, which including Baird’s Sandpiper, Pectoral Sandpiper, Semipalmated Plover, Short-billed Dowitcher, Stilt Sandpiper, White-rumped Sandpiper and Wilson’s Snipe, are all taking advantage of the mud flats, marshy areas and other new riparian habitat taking hold in the former Stump Pond site.
Fish Passage
While fish passes can mitigate against some impacts of dams, even the best don’t address all the ecological problems caused by dams and impoundments. The most simple passage structures (typically called “fish ladders”) are specifically designed to accommodate a single species, and even then, only successfully move a limited percentage of migrating fish upstream. Studies have shown that success of such fishways can range significantly, depending on their design, flow rates and ability to attract fish to enter the fishway. More advanced (and expensive) fish passes (generally called “nature-like” fishways) are designed to allow multiple species to move upstream, but also fail to achieve full passage success, even for targeted species.
Most critically, regardless of how advanced its design, no fish passage structure fully reconnects a river. If the dam remains, even with a fish passage solution in place, then it continues to impound water, increase water temperature, reduce water quality, impede sediment transport, create conditions favorable to non-native species and generally degrade habitat (both upstream and downstream).
While Seatuck has advanced the installation of fish passage structures in past decades, we have come to recognize their significant limitations. As such, our efforts have shifted to focus on dam removal as the superior tool for restoring rivers and streams and the species they support. It is a more cost-effective and successful tool for restoring the health our riverine systems and the essential ecological roles they play. There may be some unique situations, when there are compelling reasons for not pursuing dam removal, where we would support the installation of fish passage to provide benefits for specific species. However, we do not support the repair of a failed dam, even with plans to include fish passage.
Recreation
Freshwater Fishing
As discussed above, the draining of Stump Pond will reduce warm, slow-moving water that favors species such as common carp, largemouth bass, bluegill, bullhead catfish and yellow perch. As such, it will reduce the availability of recreational fishing opportunities for those interested in pursuing these species. However, some of these species, especially yellow perch, for example, will likely continue to persist in larger pools, backwaters and even brackish sections of the river system.
On the other hand, the restoration of flowing, cold-water habitat will benefit brook trout, our only native trout and an iconic sportfish, and improve and expand the existing downstream trout fishery in Caleb Smith State Park Reserve. Brook trout are part of Long Island’s history as a recreational destination. They were sought after by rich anglers from New York City and were one of the primary quarries that drove the development of the Island’s hunting & fishing clubs. If allowed to remain free-flowing, the restored reaches of the Nissequogue will provide ideal native habitat for brook trout to flourish – and support expansion of the native populations in the portions of the river both upstream and downstream from Blydenburgh County Park.
Saltwater Fishing
As outlined above, a vitally important ecological role that free-flowing rivers play is in supporting migrations of diadromous and semi-diadromous fish that spend parts of their lives in both freshwater and saltwater. These fish, from alewife to white perch to American eel, move energy up and down rivers and, in the process, provide forage for a wide variety of predators. Importantly, this includes many desirable saltwater sportfish species, such as striped bass, bluefish, weakfish and false albacore – all of which are found in Long Island Sound and are known to occur in the mouth of the Nissequogue River. A fully connected and healthy Nissequogue River would support great numbers of diadromous fish, which would, in turn, support desirable saltwater sportfish species.
Wildlife Observation
While some species, such as non-native Mute Swans, will not be as numerous in the park without Stump Pond, the overall variety and numbers of wildlife will expand with the diversification of the habitat that will occur at the former pond site. As described above, the wetland and field habitat that will establish within the river’s floodplain will attract a much greater diversity of birds, which will attract and delight birders. As the riparian meadows mature, native plants – from goldenrod to fleabane to New York aster – will attract countless butterflies, bumblebees and other pollinators for visitors to observe and enjoy.
Boating
While rowboat rentals were available and boaters could launch their own canoes/kayaks on Stump Pond, the conditions were less than ideal for boating. The heavy growth of submerged aquatic vegetation (described by one commentor as “filled with weeds shore to shore”) made it difficult to enjoy for many, especially inexperienced boaters. While open water boating opportunities would no longer be possible in the absence of Stump Pond, perhaps Suffolk County Parks and New York State Parks may consider allowing (at least occasionally) kayaks and canoes to navigate the reaches of the Nissequogue River during sufficient flows. Kayaking and canoeing are already very popular in the tidal section of the river.
Trails
The failure of the dam in Blydenburgh created an interruption of the popular Stump Pond trail loop and broke the continuity of the 32-mile Long Island Greenbelt Trail. While we agree that it is important to restore passage over the Nissequogue River for hikers, cyclists and equestrians, the endeavor need not be linked to rebuilding the dam. Clearly, a bridge over the river would allow people to resume the full use and enjoyment of the trails at Blydenburgh Park and the Greenbelt Trail. As illustrated in the rendering below, a bridge could be installed at the site of the former dam – and at a fraction of the cost of constructing a new dam.
In fact, the failure of the dam provides Suffolk County a unique opportunity to expand the trail system at Blydenburgh Park. As the former Stump Pond site dries out, the river’s natural floodplain will allow for new recreational opportunities for park visitors, including the potential for the addition of trails, boardwalks and observation platforms. As depicted in the second rendering below, the installation of pedestrian bridges over the two branches of the river would significantly expand hiking opportunities within the park, allowing visitors to access unique habitats and observe a greater diversity of plants and wildlife.
History
It is well known that the Stump Pond Dam was constructed around the turn of the 19th century to create an impoundment to power a grist and saw mill. This mill indisputably played an important part in the development of Smithtown and is part of the history of the region’s colonial development. However, the mill’s significance and history are not lost with the river reverting to its natural state. In fact, the mill house itself – the most significant part of the story – still stands on the site. While the mill house has been neglected and not used for interpretive purposes for nearly half a century, it could be restored to host public educational visits and programs, and become a centerpiece of Blydenburgh’s historic district. Regarding historical significance, it’s also important to note that the free-flowing Nissequogue River supported and was revered by Long Island’s Native American populations for thousands of years before it was dammed.
River Restoration Network
Seatuck is proud to be a member of the Long Island Sound River Restoration Network, a coalition of Connecticut and New York-based organizations dedicated to the restoration and health of our region’s rivers. The network’s new film, Reconnected, will be screened on Long Island in early 2025 – for now, enjoy the trailer below.
Big River Inspiration
These films, from both next door (Hudson River, NY) and across the county (Elwah River, WA), document the ecological restoration that comes when dams are removed and rivers are left to be rivers.
This 2020 film explores the evolution of our national attitude from pride in dams as engineering wonders to the growing awareness that our own future is bound to the life and health of wild rivers. (88 mins)
This film, which aired on PBS in 2023, explores the amazing restoration ten years after a massive dam removal on the Elwha River in Washington State. (28 mins)
Hudson Riverkeeper produced this short documentary film in 2019 to showcase their efforts to restore natural habitat by eliminating obsolete dams throughout the Hudson River Estuary. (15 mins)