Photo: U.S. Fish and Wildlife Service
Invasive species
Protecting the Hudson includes defending it against outside threats
The challenge
Aquatic invasive species threaten the ecology of the Hudson River and its tributaries by displacing, competing with, or preying on native species.
Dangerous hitchhikers
The Hudson River has been dramatically altered by nonnative species that have been introduced. Metro-North riders and kayakers will be familiar with the thick mats of water chestnuts that clog freshwater bays through the summer, and drinking water treatment plants have to contend with zebra mussels that clog their intakes. These species and others — fish, plants, mollusks, crustaceans and other forms of life — also have had profound impacts on the ecosystem, forever damaging the ability of native species to survive and thrive. Invasive species are recognized as one of the major threats to global biodiversity — and freshwater ecosystems are the most threatened of all.
These species are typically introduced unintentionally by commerce, anglers, boats that have been exposed to waters inhabited by invasive species, or people releasing unwanted aquarium fish and aquatic vegetation into our waterways. With no natural predators or other ecological processes to control their numbers, these invasive species can multiply quickly, and outcompete or overwhelm their native counterparts. Because most species can’t be eliminated once introduced, stopping the introduction of new nonnative species is the highest priority.
Scientists have warned of this threat. Repeatedly. For nearly a decade. It’s time to heed the call. Let’s seize a critical opportunity while we have it.
Dan Shapley
Senior Director of Advocacy, Policy and Planning
24%
Almost a quarter of fish species identified in the Hudson River watershed are non-native
8
It took the round goby eight years to move from the Great Lakes through the Erie Canal to the Hudson
- Focus areas
- Habitat and wildlifeWater quality
What we're doing
Riverkeeper is pushing for preventative solutions that address all types of invasive species.
Riverkeeper works closely with local partners and state agencies to develop and enact effective plans that limit or help prevent the spread of invasive species, as well as perform outreach to educate boaters, anglers, and the general public about how they can help control any looming and potential threats that may negatively impact health of the Hudson River’s ecosystems.
Shutting the door
The species that have most profoundly altered the Hudson, and which pose the greatest known threats, typically evolved to conditions on other continents and ocean away. Global shipping, which operated without protections for decades — delivered many “hitchhikers” often to the Mississippi River. Natural barriers — the mountains that separate one river system from another — would have prevented further spread, but because we built canals connecting so many major waterways, species have crossed from the Mississippi to the Great Lakes to the Mohawk and Hudson Rivers. Riverkeeper is focused on the Erie Canal as the most important pathway for species to enter and disrupt the Hudson. For canal systems, one of the most practical ways of preventing invasive species is to develop boat lift and wash stations at the points where major watersheds used to be naturally separated. These dry stations disconnect the waterway where boats can be lifted, inspected, and washed — a practice that effectively blocks a variety of species including fish, plants, molluscs, crustaceans, and even certain pathogens.
This technology already exists, and we are urging the state to implement these measures in our canal system as a key tool to prevent the spread of invasives and help protect the Hudson River ecosystem.
Round goby
Photo: CC, Peter Halasz
Native to the Black and Caspian seas, round goby were first found in the Hudson in 2021, after being discovered in the Erie Canal in 2013, and before that the Mississippi River and the Great Lakes. Goby are voracious feeders that spawn multiple times each year and thus outcompete native species for food and spawning habitat. Among other things, they consume the eggs of native fish species. These invasive fish also carry and spread pathogens such as Viral Hemorrhagic Septicemia (VHS), which has already led to large fish kills in New York State waters. Riverkeeper is working with partners to advocate for effective engineering solutions to stop the further spread of Round Goby through the Upper Hudson River and Champlain Canal.
Water chestnuts
Photo: Department of Environmental Conservation
Native to Eurasia and introduced to the U.S. as an ornamental in the 1800s, water chestnuts are now widely established throughout the Hudson Valley. These plants form leafy mats that root in streambeds, choke waterways, and block sunlight from native submerged vegetation. The mats grow so thick that they impede the passage of kayaks and other watercraft, impair habitat quality for native species, and the spiny seed pods of water chestnuts can injure people stepping on them when wading or swimming. The freshwater shallows that water chestnut inhabit were once filled with water celery and other “submerged aquatic vegetation” (SAV). These remaining shallow SAV beds are one of the most important native habitats.
Riverkeeper advocates for the management of water chestnuts through manual or mechanical removal. In places where water chestnut create mats, such as Schodack Island, we advocate for side-channel cuts to increase water flow, which will inhibit the rampant growth of water chestnuts. When the river can “breathe,” it can remove these water chestnuts of its own accord.
Hydrilla
Photo: CC, USFWs Pacific
Hydrilla is an Asian species of aquatic plant that was first discovered in Orange County in 2008. It has since spread to 11 other counties including Westchester, where it has recently established several “hot spots” in the Croton River, a tributary to the Hudson. Hydrilla grows rapidly, forming large mats that clog infrastructure and impede natural stream flow, damage habitat by displacing natural vegetation, and decrease oxygen essential to the survival of fish and other aquatic life. If hydrilla were to spread in the Hudson, it would likely impact large areas of the river and magnify some of the same impacts caused by water chestnuts, as it can root in much deeper water than water chestnut — making it a high priority to contain and eradicate hydrilla infestations before they spread. Riverkeeper has been involved in supporting New York State and New York City’s efforts to kill hydrilla before they spread further from the Croton River.
Zebra mussels
Photo: Minnesota Department of Natural Resources
Zebra mussels are native to Eurasia and were introduced to the Great Lakes via European cargo ships in the 1980s, eventually reaching the Hudson River in 1991 via the Erie Canal. These filter-feeding mollusks spread rapidly, clogging boat engines and infrastructure, and contributing to the decline of shad and herring populations. Voracious filter feeders, zebra mussels consume many of the same plankton that young of year shad and herring rely on.
The zebra mussel population, though still significant in the Hudson River, has been in a decline for 20 years — without chemical or biological intervention. Native species are learning to use zebra mussels as a potential food source.
Carp
Photo: CC, Peter Halasz
In addition to the grass carp, which the DEC is managing by releasing sterile grass carp into New York waters to reduce their numbers, more species of carp that originated in Asia are present in the Mississippi River system, and some evidence suggests they have reached the Great Lakes. Silver, bighead, and black carp would have different impacts on the Hudson — each likely significant. Some leap from the water in large numbers, presenting a danger to boaters, while others consume plankton or other species that native fish rely on. In the Illinois River, invasive carp have come to dominate the ecosystem. Scientists warned in a 2013 New York Times op-ed to “beware the marauding carp” by preventing their spread through the Erie Canal. Riverkeeper is advocating for New York State to take that advice before it’s too late.
What can you do?
- Check your boating and fishing equipment for invasive species
- Clean any visible mud, plants, fish or animals before transporting equipment
- Discard items in an upland area or in one of the invasive species disposal stations that have been installed at many boat launch sites
- Drain all water holding compartments including live wells, bait wells and bilge areas
- Dry or disinfect boats, trailers and equipment before use in another waterbody
Related campaigns
Protecting and restoring habitats
The Hudson River watershed is home to a breathtaking diversity of life. Protecting and restoring our aquatic habitats is critical for their renewal and for a healthy future for all life in the watershed
Saving Hudson River fish
Protecting iconic species vital to our local ecosystems
Water quality monitoring
Riverkeeper is the go-to source for information about the quality of the water along the Hudson River and its tributaries