Tidal River

The Hudson River from Storm King Mountain
Andy Finton

Estuarine Subtidal
State Protection
Not Listed
Not listed or protected by New York State.
Federal Protection
Not Listed
State Conservation Status Rank
Vulnerable in New York - Vulnerable to disappearing from New York due to rarity or other factors (but not currently imperiled); typically 21 to 80 populations or locations in New York, few individuals, restricted range, few remaining acres (or miles of stream), and/or recent and widespread declines.
Global Conservation Status Rank
Apparently Secure globally - Uncommon in the world but not rare; usually widespread, but may be rare in some parts of its range; possibly some cause for long-term concern due to declines or other factors.


Did you know?

Although it has not been confirmed, the Hudson River is purported to be the world's longest tidal river, reaching 150 miles. The Hudson River is home to both the shortnose and Atlantic sturgeon. Their appearance today is almost the same as when dinosaurs walked the earth during the Triassic period, 245 to 208 million years ago. They are among the oldest living fish species. You can find more information on our sturgeon conservation guides.

State Ranking Justification

This community is restricted to tidally influenced areas of the state. There is one large occurrence (Hudson River) and several small examples known from Long Island (e.g., Nissequogue and Carmans rivers). Tidal rivers are moderately threatened by pollution, shoreline development, dredging, commercial shipping, recreational overuse, and invasive species.

Short-term Trends

The number and acreage of tidal rivers in New York have proabably become stable in recent decades. The quality of the water in tidal rivers has probably improved in recent decades.

Long-term Trends

The number and acreage of tidal rivers in New York have probably declined moderately from historical numbers likely correlated with shoreline development and dredge spoil deposition. Water pollution was a very serious threat several decades ago, but has improved with the advent of pollution control facilities and regulations.

Conservation and Management


The Hudson River is recovering from several hundred years of pollution, shoreline development, dredging, commercial shipping, recreational overuse, and invasion by exotic species. Smaller tidal rivers on Long Island have had similar impacts, but at a smaller scale.

Conservation Strategies and Management Practices

Where practical, establish and maintain a riparian buffer to reduce storm-water, pollution, and nutrient run-off, while simultaneously capturing sediments before they reach the river. Buffer width should take into account the erodibility of the surrounding soils, slope steepness, and current land use. If possible, minimize the number and size of impervious surfaces in the surrounding landscape. Avoid habitat alteration within the river and surrounding landscape. For example, roads should not be routed through the riparian buffer area. If the river must be crossed, then bridges are preferred over filling and culverts. Restore past impacts, such as removing obsolete impoundments and ditches in order to restore the natural hydrology. Prevent the spread of invasive exotic species into the river through appropriate direct management, and by minimizing potential dispersal corridors.

Development and Mitigation Considerations

When considering road construction and other development activities minimize actions that will change what water carries and how water travels to this community, both on the surface and underground. Water traveling over-the-ground as run-off usually carries an abundance of silt, clay, and other particulates during (and often after) a construction project. While still suspended in the water, these particulates make it difficult for aquatic animals to find food; after settling to the bottom of the wetland, these particulates bury small plants and animals and alter the natural functions of the community in many other ways. Thus, road construction and development activities near this community type should strive to minimize particulate-laden run-off into this community. Water traveling on the ground or seeping through the ground also carries dissolved minerals and chemicals. Road salt, for example, is becoming an increasing problem both to natural communities and as a contaminant in household wells. Fertilizers, detergents, and other chemicals that increase the nutrient levels in wetlands cause algae blooms and eventually an oxygen-depleted environment where few animals can live. Herbicides and pesticides often travel far from where they are applied and have lasting effects on the quality of the natural community. So, road construction and other development activities should strive to consider: 1. how water moves through the ground, 2. the types of dissolved substances these development activities may release, and 3. how to minimize the potential for these dissolved substances to reach this natural community.

Inventory Needs

Survey for occurrences on Long Island to advance documentation and classification of tidal rivers. Inventory remaining rivers that are in good condition (A- to AB-ranked).

Research Needs

Collect sufficient quantitative data to support the recognition of several distinct tidal rivers based on salinity and characteristic flora and fauna (e.g., saltwater tidal river, brackish tidal river, and freshwater tidal river).

Rare Species

  • Acipenser brevirostrum (Shortnose Sturgeon) (guide)
  • Acipenser oxyrinchus (Atlantic Sturgeon) (guide)
  • Ardea alba (Great Egret) (guide)
  • Bolboschoenus novae-angliae (New England Bulrush) (guide)
  • Lampsilis cariosa (Yellow Lampmussel) (guide)
  • Libellula needhami (Needham's Skimmer) (guide)
  • Menidia beryllina (Inland Silverside) (guide)
  • Menidia menidia (Atlantic Silverside) (guide)
  • Potamogeton diversifolius (Southern Snailseed Pondweed) (guide)
  • Rallus elegans (King Rail) (guide)
  • Strongylura marina (Atlantic Needlefish) (guide)
  • Stylurus plagiatus (Russet-tipped Clubtail) (guide)


New York State Distribution

The range of this community corresponds to the tidal range of the Hudson River (i.e., from the river mouth at New York City upstream about 150 miles to the Troy Dam), and the tidal range of the smaller tidal rivers of Long Island.

Global Distribution

Freshwater tidal rivers similar to those in New York occur on the Atlantic Coastal Plain from Maine to North Carolina.

Best Places to See

  • Rockefeller State Park Preserve (Westchester County)
  • Hudson River Estuary (Greene, Ulster Counties)
  • Tallman Mountain Sate Park (Rockland County)
  • Bear Mountain State Park (Rockland County)
  • Hudson River Islands State Park (Rockland County)
  • Bristol Beach State Park (Rockland County)

Identification Comments

General Description

The aquatic community of continuously flooded substrates that support no emergent vegetation. Within the river there are two zones; the deepwater zone includes areas in which substrates are usually over 2 m (6 feet) deep at low tide, the shallow zone includes submerged areas less than 2 m (6 feet) deep at low tide that lack rooted aquatic vegetation. In the river there is a vertical salinity gradient, with a surface layer of fresh water (with salinity values less than 0.5 parts per thousand) floating over a deeper layer of brackish water (with salinity values between 0.5 and 18.0 parts per thousand). Salinity values at any one place in the river may fluctuate as the tides flow in and out because the "salt wedge" of brackish water alternately rises and falls with the tides (Edinger et al. 2002).

Characters Most Useful for Identification

A large river, such as the Hudson River, that has a salinity gradient (i.e., very salty at the river mouth, brackish upstream, and freshwater inland), and shows evidence of two daily tides along the shoreline.

Best Time to See

Tidal rivers are observable year round. The powerful and nourishing spring flood can be observed at snow melt in March and April. The flora on the margins of the river can be observed throughout the growing season. Ice floes that move down the channel can be seen in the winter. Bird migration is prominent along the Hudson River in April and May.

Tidal River Images


Characteristic Species

  • Emergent aquatics

    • Heteranthera reniformis (mud-plantain)
    • Potamogeton perfoliatus (clasping-leaved pondweed)
    • Vallisneria americana (water-celery, tape-grass)
  • Submerged aquatics

    • Ceratophyllum demersum (common coon-tail)
    • Elodea nuttallii (Nuttall's waterweed)
    • Najas guadalupensis (Guadalupe water-nymph, Guadalupe naiad)
    • Potamogeton perfoliatus (clasping-leaved pondweed)
    • Stuckenia pectinata (Sago pondweed)

Similar Ecological Communities

  • Freshwater tidal creek (guide)
    Tidal creeks are smaller than tidal rivers. Tidal creeks drain the waters of tidally flooded marshes. Freshwater tidal creeks often flow in a sinuous (i.e., meandering) channel through a freshwater marsh.
  • Saltwater tidal creek (guide)
    Tidal creeks are smaller than tidal rivers. Tidal creeks drain the waters of tidally flooded marshes. Most saltwater tidal creeks flow in a sinuous (i.e., meandering) pattern through a salt marsh.
  • Unconfined river (guide)
    Unconfined rivers are not tidal.



Percent cover

This figure helps visualize the structure and "look" or "feel" of a typical Tidal River. Each bar represents the amount of "coverage" for all the species growing at that height. Because layers overlap (shrubs may grow under trees, for example), the shaded regions can add up to more than 100%.

Additional Resources


Boyce Thompson Institute for Plant Research. 1977. An Atlas of the Biologic Resources of the Hudson Estuary. Yonkers, New York. 104 pp.

Cole, Jonathan J., Stuart Findlay and Michael L. Pace. 1988. Basic ecosystem processes in the Hudson River: A Report of a Conference at the Institute of Ecosystem Studies, October 11 and 12, 1988. Unpublished Report.

Darmer, Kenneth I. 1987. Overview of Hudson River Hydrology. Final report to the Hudson River Foundation. 174 pp.

Edinger, G. J., D. J. Evans, S. Gebauer, T. G. Howard, D. M. Hunt, and A. M. Olivero (editors). 2014. Ecological Communities of New York State. Second Edition. A revised and expanded edition of Carol Reschke’s Ecological Communities of New York State. New York Natural Heritage Program, New York State Department of Environmental Conservation, Albany, NY. https://www.nynhp.org/ecological-communities/

Edinger, Gregory J., D.J. Evans, Shane Gebauer, Timothy G. Howard, David M. Hunt, and Adele M. Olivero (editors). 2002. Ecological Communities of New York State. Second Edition. A revised and expanded edition of Carol Reschke's Ecological Communities of New York State. (Draft for review). New York Natural Heritage Program, New York State Department of Environmental Conservation. Albany, NY. 136 pp.

Findlay, Stuart, Elizabeth A. Blair, William C. Nieder, Eugenia Barnaba and Susan Hoskins. 1997. Distribution of submerged rooted vegetation beds of the tidal Hudson River. Unpublished report. Institute of Ecosystems Studies. Millbrook, New York. 15 pp.

Gladden, John B., Frank R. Cantelmo, J.M. Croom and R. Shapot. 1988. Evaluation of the Hudson River ecosystem in relation to the dynamics of the fish populations. American Fisheries Society Monograph 4: 37-52.

Johnsen, John H. 1976. The Hudson River Guide. A Geological and Historical Guide to the Lower and Mid-Hudson Valley Region, as Viewed from the River. Unpublished Report. New York State Geological Association. October 15-17, 1976.

Kiviat, Erik and Gretchen Stevens. 2001. Biodiversity assessment manual for the Hudson River Estuary Corridor. New York State Department of Environmental Conservation. Albany, NY.

Mills, Edward L., Mark D. Scheuerell, James T. Carlton and David L. Strayer. 1997. Biological invasions in the Hudson River basin. New York State Museum Circular no. 57.

Moran, Mary Ann and Karin E. Limburg. 1986. The Hudson River Ecosystem. p. 6-39. In K.E. Limburg, M.A. Moran and W.H. McDowell. The Hudson River Ecosystem. Springer-Verlag, New York.

New York Natural Heritage Program. 2024. New York Natural Heritage Program Databases. Albany, NY.

New York State Department of Environmental Conservation. No date. The Hudson River Estuary Action Plan. New York State Department of Environmental Conservation. Albany, NY.

New York State Department of State, Division of Coastal Resources and Waterfront Revitalization and The Nature Conservancy. 1990. Hudson River Significant Tidal Habitats: A guide to the functions, values, and protection of the river's natural resources. New York State Department of State, Albany, NY. 184 pp.

Reschke, Carol. 1990. Ecological communities of New York State. New York Natural Heritage Program, New York State Department of Environmental Conservation. Latham, NY. 96 pp. plus xi.

Schmidt, Bob. 1996. Migratory fishes and Hudson River tributaries. News from Hudsonia 12 (1): 1-5.

Schmidt, Robert E. and Susan Cooper. 1996. A catalog of barriers to upstream movement of migratory fishes in Hudson River Tributaries. Hudsonia Ltd., Bard College Field Station, Annandale, New York. 185 pp.

Swinn, Brian W. 2000. The Hudson Reborn. Access is improved along the river. New York State Conservationist, April: 2-5.

United States Department of Commerce NOAA. 1982. Draft environmental impact statement. Hudson River Estuarine Sanctuary. New York State Department of Environmental Conservation. Albany, NY. 147 pp.


About This Guide

This guide was authored by: Jennifer Garrett

Information for this guide was last updated on: November 15, 2023

Please cite this page as:
New York Natural Heritage Program. 2024. Online Conservation Guide for Tidal river. Available from: https://guides.nynhp.org/tidal-river/. Accessed July 19, 2024.