Hudson River National Estuarine Research Reserve, New York

Source: NOAA


The Hudson River is an amazing resource: a tidal river that links the communities of the valley economically, culturally and ecologically, and a cradle of human development for thousands of years. Home to more than 200 species of fish, the Hudson serves as a nursery ground for such important fish as sturgeon, striped bass and American shad. It also supports a corresponding abundance of other river-dependent wildlife, especially birds.

The river is profoundly influenced by the ocean's tides for over half its length, creating an estuary which stretches 153 miles and includes a wide range of wetland habitats. The reserve sites reflect this diversity, from the brackish marshes of Piermont to the slightly brackish wetlands of Iona Island, and the freshwater tidal mudflats and marshes of Tivoli Bays and Stockport Flats.

The Hudson River Reserve is part of the National Estuarine Research Reserve System (NERRS), a network of estuarine habitats protected and managed for the purposes of long-term research, education, and coastal stewardship. Established by Congress in 1972 as part of the Coastal Zone Management Act (CZMA), the NERRS is administered as a partnership between the National Oceanic and Atmospheric Administration (NOAA) and the coastal states.

Stockport Flats

caption Hudson River Reserve stockport flats boundary map. (Source: NERRS)

Stockport Flats is the northernmost site in the Hudson River Reserve. It is located on the east shore in Columbia County, a few miles north of the city of Hudson, in the towns of Stockport and Stuyvesant.

The Stockport Flats site is a five-mile, narrow mosaic of landforms, including from north to south Nutten Hook, a bedrock outcropping; Gay's Point and Stockport Middle Ground Island, dredge features that are both part of the Hudson River Islands State Park; the mouth of Stockport Creek, a large tributary stream; a portion of the upland bluff south of Stockport Creek; the dredge spoils and tidal wetlands between Stockport Creek and Priming Hook; and the northern end of Priming Hook. The Hudson is entirely tidal freshwater at this site.

Stockport Flats is dominated by freshwater tidal wetlands, including subtidal shallows, intertidal mudflats, intertidal shores, tidal marshes and floodplain swamps.

Stockport Creek drains a watershed of about 500 square miles.


Flora: The site's subtidal shallows support communities of submerged plants, with water celery most abundant. The tidal marshes are dominated by narrowleaf cattail, wild rice, spatterdock and pickerelweed. Tidal and floodplain swamps are dominated by a mixture of deciduous forest characteristic of river bottoms.

Fauna: Stockport Flats provides spawning and/or nursery ground for anadromous and freshwater fish species including alewife, blueback herring, American shad, rainbow smelt, striped bass and smallmouth bass. Waterfowl use the site as both a migrational staging area and a wintering ground. Wading, shore and song birds use it for feeding and breeding. Bank swallows and belted kingfishers nest in the sand cliffs on the southwest shore of Stockport Middle Ground.

Endangered Species: Rare species found at Stockport Flats include bald eagles, osprey, heart leaf plantain, estuary beggar ticks, kidney leaf mud-plantain and spongy arrowhead.

Tidal Range and River Flow

The average tidal range at Stockport Flats is 4.0 feet. Stockport Creek, one of the 10 largest tributaries to the lower Hudson, is a substantial inflow to the site. The Hudson is entirely fresh water at this site.


Stockport Flats is part of the Hudson-Mohawk Lowlands physiographic region, made up of Cambrian and Ordovician bedrock. Soils in the area are primarily glacial till and Lake Albany clays, with substantial areas of sandy dredge soil deposits. Soils at Stockport Flats include frequently flooded soils. In addition, fine sandy loam is found at the boat launch on the north shore of the mouth of Stockport Creek. Sandy loams and gravelly sandy loams are found on Nutten Hook. Areas of sandy beach are found on Stockport Middle Ground and Gay's Point, where human traffic and wave action have eradicated intertidal vegetation.

Cultural History

Native Americans inhabited the Hudson River Estuary corridor, some more than 5,000 years ago. Several archaeological sites have been scientifically excavated and documented across the river from Stockport, but none on the site itself. Because Nutten Hook is a bedrock promontory, this site may well have had archaeological significance. In the early 19th century the area's primary industries were transportation (rail and ship) and agriculture (crops and milling.) Brick manufacturing and ice houses were important industries of the late 19th and early 20th centuries.

The upper Hudson was the center of the ice industry during the last half of the 19th century. Nutten Hook was the site of the R&W Ice Company (c. 1885), which was one of the largest independently-owned ice houses on the Hudson River, now on the National Register of Historic Places. With portions of the foundations and the powerhouse chimney remaining, this site is the most intact and interpretable ruin associated with the ice industry on the Hudson River.

Tivoli Bay

caption Hudson River Reserve Tivoli Bay boundary map. (Source: NERRS)

The Tivoli Bay component extends for two miles along the east shore of the Hudson River between the villages of Tivoli and Barrytown, in the Dutchess County town of Red Hook. The Tivoli Bay's site includes two large coves on the east shore of the Hudson River including Tivoli North Bay, a large intertidal marsh and Tivoli South Bay, a large, shallow cove with mudflats exposed at low tide. The site also includes an extensive upland buffer area bordering North Tivoli Bay; sections of upland shoreline along Tivoli South Bay; Cruger Island and Magdalene Island, two bedrock islands, extensive subtidal shallows; and the mouths of two tributary streams, the Stony Creek and the Saw Kill.

Habitats include freshwater intertidal marsh, open waters, riparian areas, subtidal shallows, mudflats, tidal swamp and mixed-forest uplands.

The Stony Creek has a watershed area of 22.2 square miles draining into Tivoli North Bay, and the Saw Kill has a watershed of 22.0 square miles draining into Tivoli South Bay.


Flora: Freshwater tidal marshes at Tivoli North Bay are dominated by narrowleaf cattail, spatterdock and invading purple loosestrife and common reed. Subtidal shallows support communities of submerged plants similar to those described for Stockport Flats and freshwater intertidal mudflats and shore communities are also present. Tivoli South Bay is dominated by Eurasian water chestnut, a floating, exotic species. Both the tidal swamp between the bays and the smaller swamp at the mouth of Stony Creek are mixed deciduous communities with well-developed shrub layer and abundant moss species. The clay bluffs and rocky islands support mixed forests dominated by oak, hickory, eastern hemlock and pine.

Fauna: This site is important spawning and/or nursery ground for a variety of anadromous and freshwater fish species. A large snapping turtle population exists in and around Tivoli North Bay. Waterfowl use the site extensively during migration and winter. Many other birds use the site for feeding, breeding and migratory stopovers. Zebra mussels, an invading exotic species, dominates subtidal rocky areas.

Endangered Species: Rare animals that occur or that have occurred at Tivoli Bays include osprey, bald eagles, king rail, least bittern, golden eagles, map turtles and American brook lamprey. Rare plants that occur or that have occurred here include heart leaf plantain, estuary beggar ticks, golden club, ovate spikerush, Parker's pipewort, Nuttall's micranthemum, Eaton's burmarigold, false pimpernel, winged monkey flower and swamp lousewort.

Tidal Range and River Flow

The Hudson is tidal freshwater at the Tivoli Bays, with an average tidal range of 3.9 feet.

The Stony Creek drains into Tivoli North Bay and the Saw Kill drains into Tivoli South Bay. Tivoli North Bay's predominantly intertidal marsh has a well-developed network of tidal creeks and pools. A similar network of creeks and pools is beginning to form in Tivoli South Bay's shallows and mudflats.


Tivoli Bays lies in the Hudson-Mohawk Lowlands physiographic region. Bedrock is Ordovician gray sandstone and shale. Upland soils in the area are primarily derived from glacial till and Lake Albany clays. Soils at the site include muck, made land and a variety of loams, including silty clay, silt, fine sandy and gravelly loams. The bottom of the bays is largely soft muck, as much as 25 feet deep. The tidal swamp between North and South Bay has eight feet of peat overlying silt.

Cultural History

Native Americans inhabited the Hudson River Estuary corridor more than 5,000 years ago, and archaeological sites have been excavated within this component. The primary industries in the area in the 18th and early 19th centuries were transportation (rail and ship) and agriculture (crops and milling). Brick manufacturing was an important early 19th century industry. By the end of the 19th century extensive portions of the shoreland had been converted to large estates, many of them still standing today.

Iona Island

caption Hudson River Reserve Iona Island boundary map. (Source: NERRS)

Iona Island is located in the Town of Stony Point in Rockland County, six miles south of West Point. Iona Island is a bedrock island in the midst of the Hudson Highlands, bordered to the west and the southwest by Salisbury and Ring Meadows, two large tidal marshes, the mouth of Doodletown Bight, an expanse of shallows and mudflats.

A separate island, Round Island, was attached to the south end of Iona Island with fill in the early 20th century. The marshes and shallows occupy one mile between Iona Island and the west shore. In addition to being part of the Hudson River National Estuarine Research Reserve, Iona Island and its associated tidal wetlands have been designated a National Natural Landmark by the National Park Service.

The component is comprised of brackish intertidal mudflats, brackish tidal marsh, freshwater tidal marsh and deciduous-forested uplands.

Doodletown Brook is the principal tributary to the site, draining approximately 2.9 square miles. The Iona Island Component encompasses 556 acres.


Flora: The vegetation in Iona Island's marshes is dominated by narrowleaf cattail, with moderate amounts of common reed and swamp rose mallow. There is a healthy stand of crack willow in one small area of tidal swamp at the mouth of Doodletown Brook. The island and mainland slopes are covered with deciduous forest, with abundant red oak, chestnut oak and pignut hickory. Substantial areas of Iona Island's tidal shallows are bare mud, although water celery and other submerged plants also occur there. Brackish intertidal mudflats, brackish tidal marsh and freshwater tidal marsh are all present.

Fauna: Many bird species breed within the site. Herons and shorebirds feed in and around the marshes and the areas is recognized as a waterfowl concentration area. Muskrat and mink, amphibians (in non-tidal areas), snapping turtles and blue claw crab are also found there. Offshore shallows are used for spawning and/or nursery for anadromous and resident freshwater fishes, including alewife, blueback herring, white perch and striped bass.

Endangered Species: Rare animals found at or offshore Iona Island include least bittern, bald eagles, golden eagles, osprey, peregrine falcon, shortnose sturgeon and five-lined skink. Rare plants include a sedge, wooly lip-fern, Parker's pipewort, slender knotweed, spongy arrowhead, saltmarsh bulrush and pigmyweed.

Tidal Range and River Flow

The tidal range at the Iona Island Component is 2.8 feet. Doodletown Brook flows into the Components estuarine waters.

Geology and Soils

Bedrock at Iona Island is mostly Precambrian gneiss. The rock is very resistant to erosion and forms the rocky knobs of Iona that project 100 feet above the river. The same steep slopes dive down under the marshes, and sediments are more than 100 feet thick.

Cultural History

Existing evidence indicates that Native Americans occupied the island as much as 5,500 years ago. Archaeological sites have been scientifically excavated and documented on Iona Island. Artifacts are on display at the Bear Mountain Trailside Museum and Zoo, one mile north of the site.

Europeans originally settled on Iona Island in 1683. Although the site was not used for commercial purposes until the mid-19th century, by the time of the Civil War, Iona Island was producing a substantial amount of commercially grown fruit. During the Civil War, the island was converted to a resort hotel. In 1899, the U.S. Navy purchased Iona Island for use as a munitions depot through World War II. In 1965, the Palisades Interstate Park Commission (PIPC) purchased the island for use as a recreation area and bird sanctuary.

Piermont Marsh

caption Hudson River Reserve Piermont Marsh boundary map. (Source: NERRS)

This component encompasses 1,017 acres. The site lies at the southern edge of the village of Piermont, four miles south of Nyack.

The Piermont Marsh is located on the west shore of the Tappan Zee in the town of Orangetown, in Rockland County. The site occupies two miles of shoreline south of the mile-long Erie Pier and includes the mouth of Sparkill Creek and extensive tidal shallows.

Piermont marsh habitats include brackish tidal marsh, shallows and intertidal flats. The Sparkill Creek drains 11.1 square miles of watershed.


Flora: Emergent marshes are dominated by narrowleaf cattail and common reed, with lesser amounts of salt water cordgrass, salt meadow cordgrass, spikegrass and swamp rose mallow. Substantial parts of offshore shallows are bare mud, although submerged plants are also present. Water celery, curlyleaf pondweed, sago pondweed and horned pondweed are found in the shallows. The forest at the base of the Palisades Ridge has abundant and large beech trees, tulip trees, red oaks, black birches and flowering dogwoods.

Fauna: The mudflats are used extensively by herons and egrets. Waterfowl, wading birds and shorebirds feed in the area during migration. Large numbers of resident and breeding bird species, blue claw crabs, resident fishes, snapping turtles and diamondback terrapins are also present.

Endangered Species: Rare species found at Piermont Marsh include least bittern, osprey, bald eagle, peregrine falcon and diamondback terrapin. Rare plants include a sedge, button-bush dodder and saltmarsh bulrush.

Tidal Range and River Flow

The average tidal range at the component is 3.2 feet. The Sparkill Creek discharges into the north end of the marsh at the component.


The west shore of Piermont Marsh is formed by part of the Palisades Ridge, a flat-topped, 150-foot-high cliff and siderock formation. The cliff is Triassic diabase, a hard igneous rock between 210 and 245 million years old, underlain by Triassic sandstone and shale. Sparkill Gap, the valley of Sparkill Creek, just west of the north end of the Piermont Marsh, is the only sea level break in the Palisades Ridge.

Sediments present at the Piermont site are peat and organic silt. These deposits are at least 40 feet deep in the western part of the marsh, which has been developing for nearly 5,000 years. Soils on the shore near the site are derived from glacial till. These are shallow and acid, with deeper and richer pockets close to the marsh. A few well-defined but relatively shallow tidal creeks cut the marsh. Piermont Marsh is located at the south end of the broad and shallow Tappan Zee, and extensive shallows border the east side of the marsh.

Cultural History

Native Americans inhabited the Hudson River Estuary corridor more than 5,000 years ago, but no prehistoric sites have been excavated at the component to date. The first mile of Sparkill was navigable to the flat bottomed sloops of the 18th century. During this period, the creek was used as the principal entry port on the west side of the lower Hudson Valley. The port was the major access route to the fur and timber country lying to the west and a convenient shipping point for the agricultural industries (crops and milling) of the local area.

By the early 19th century, development of larger sloops with deeper drafts made use of Sparkill Creek impractical. To solve this problem the mile-long pier was constructed in 1839 at the terminus of the Erie railroad. The pier still stands today and is used by local residents for access to the Hudson River. The pier has likely had a significant impact on development of the marsh by accelerating deposition of sediments.


caption Hudson River Reserve research. (Source: NERRS)

Research efforts are focused on generating the information necessary for management and protection of the estuary.

The reserve provides a wealth of opportunities for comparative, descriptive and quantitative studies of ecological patterns and processes due to the following physical and chemical characteristics of the Hudson River estuary: (1) freshwater to brackish conditions exist along the Hudson River estuary; (2) a gradient of generally increasing urban development exists along the Hudson River from north to south; (3) hydrological exchange studies can be conducted between the marshes and the Hudson River through restricted openings in railroad embankments; and (4) natural and anthropogenic tracers can be used to describe the movement of particles through the system.

Research support is provided through three fellowship programs co-sponsored by the reserve, which provides financial support for graduate and undergraduate students to conduct research in the reserve sites. These fellowships have generated well over 100 student research projects in the past 20 years.

Much of the reserve-sponsored research is centered on better understanding the aquatic habitats of the Hudson River estuary. Current ongoing projects include the: (1) inventory and ecological assessment of submerged plant beds; (2) mapping and assessment of the benthic habitats of the Hudson River estuary; and (3) ecological functional assessment of freshwater tidal wetlands. Research that will increase our understanding of functional gains in aquatic habitat restoration is also critical. In this regard, the reserve is investigating the ecological response of tidal marshes to the removal of common reed (Phragmites australis) and the ecological implications of removing tributary dams and/or installing fish passageways.

In addition to the NERRS System-Wide Monitoring Program, a long-term environmental monitoring program is being carried out to support both research and management at the reserve. Surface water quality, atmospheric conditions and marsh plant communities have been monitored on a regular basis since 1991. Changes detected over this time period have been used to direct research and guide management decisions.

Further Reading

Disclaimer: This article is taken wholly from, or contains information that was originally published by, the National Oceanic and Atmospheric Administration. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the National Oceanic and Atmospheric Administration should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.



(2008). Hudson River National Estuarine Research Reserve, New York. Retrieved from


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