Text modified from Abell et al. 2000. Freshwater Ecoregions of North America: A Conservation Assessment. Island Press, Washington, DC, USA. Additional text provided by Jennifer Hales.<
Major Habitat Type
Temperate coastal rivers
Drainages flowing into
The Chesapeake Bay drainage flows to the Atlantic Ocean.
Main rivers to other water bodies
Major rivers in the southern portion of the ecoregion include the Potomac and Rappahannock rivers. Rivers originating on the Delmarva Peninsula include the Sassafras, Chester, Choptank, and Nanticoke. The largest tributary to the Chesapeake is the Susquehanna River, contributing 50% of the freshwater in the Bay. The headwaters of the Susquehanna originate on the Appalachian Plateau. Together, the Susquehanna and its tributaries cut through select mountain ridges of the Ridge and Valley province on their way to the Piedmont Plateau. Unlike the other major rivers in this ecoregion, the Susquehanna does not reach the Coastal Plain until just before its confluence with the Chesapeake itself.
The extent of this ecoregion is defined by the river drainages of the Chesapeake Bay. The ecoregion covers most of northern Virginia, the eastern extension of West Virginia, most of Maryland, part of southwestern Delaware, roughly the central one-third of Pennsylvania, and part of western New York.
The ecoregion includes the Appalachian Plateau and Ridge and Valley physiographic provinces in the western and northern portions of the ecoregion, the Piedmont Plateau in the south central portion, and the Atlantic Coastal Plain in the southeastern portion of the ecoregion. Elevation ranges from sea level to over 1400 m.
The Chesapeake Bay represents the largest estuary in the United States, and its drainage includes a diversity of wetlands, marshes, riparian forests, rivers and streams.
The Chesapeake Bay ecoregion spans six terrestrial ecoregions that includes coastal forests and temperate broadleaf and mixed forests. Hemlock (Tsuga canadensis) and beech (Fagus grandifolia) once dominated the presettlement forests of the Allegheny Highlands, whereas massive tulip poplars (Liriodendron tulipifera), chestnuts (Castanea dentata), red spruce (Picea rubens), and oaks (Quercus spp.) once dominated the mid-elevations of the Appalachian/Blue Ridge forests. The Northeastern coastal forests are characterized by white oak (Quercus alba) and northern red oak (Q. rubra). Around the mouth of the Bay, Southeastern mixed forests and Mid-Atlantic coastal forests are the predominant vegetation types (Ricketts et al. 1999).
Description of endemic fishes
The only endemic is the Maryland darter (Etheostoma sellare), restricted to one small section of a stream in central Maryland.
Justification for delineation
Ecoregion boundaries are modified from Abell et al. (2000), which based its units on subregions defined by Maxwell et al. (1995). Modifications to this ecoregion were made following recommendations from the Endangered Species Committee of the American Fisheries Society. The James River was moved from the Chesapeake Bay to the Appalachian Piedmont  based on a dissimilarity analysis that showed greater faunal similarities between the James and rivers south of it than those to the north and in the Chesapeake Bay ecoregion.
- McNab, W. H. and Avers, P. E. (1994) \Ecological subregions of the United States\ U.S. Forest Service, ECOMAP Team, WO-WSA-5. Online. http://www.fs.fed.us/land/pubs/ecoregions/index.html..
- Ricketts, T. H.,E. Dinerstein,D.M Olson;C.J. Loucks (1999). "Terrestrial ecoregions of North America: A conservation assessment" Washington, D.C.: World Wildlife Fund.
- Abell, R.,Olson, D.,Dinerstein, E.,Hurley, P. T.,Diggs, J. T.,Eichbaum, W.,Walters, S.,Wettengel, W.,Allnutt, T.,Loucks, C. J.;Hedao, P. (2000). "Freshwater ecoregions of North America" Washington, D.C.: Island Press.
- Maxwell, J. R., Edwards, C. J., Jensen, M. E., et al. (1995) \A hierarchical framework of aquatic ecological units in North America (Nearctic Zone)\ St. Paul, MN. North Central Forest Experiment Station, USDA Forest Service.
- Köppen, W. (1936). "Das geographische System der Klimate" Köppen W. and R. Geiger (Ed.) Handbuch der. Klimatologie ( (Vol. 1, pp. 1–44 ) Berlin, Germany: Gebrüder Borntröger.