Lower Mississippi




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.


United States

Major Habitat Type

Temperate floodplain rivers and wetlands

Drainages flowing into

The Lower Mississippi drains an area from the Appalachian to the Ozark and Ouachita mountains, and empties into the Gulf of Mexico (Robison 1986).

Main rivers to other water bodies

Other major rivers include the lower reaches of the Arkansas and White rivers in Arkansas, the Big Black River in Mississippi, and the Tensas River in Louisiana.



The Lower Mississippi is defined by the mainstem Mississippi below its confluence with the Ohio River. The entire ecoregion lies within the lowland Gulf Coastal Plain, and the Fall Line constitutes its northern boundary (Robison 1986). The ecoregion ranges across parts of southwestern Kentucky, southeastern Missouri, western Tennessee, eastern Arkansas, most of Mississippi, and the eastern half of Louisiana.


Structurally, the Lower Mississippi is a trough between the Appalachians to the east and the Ozark and Ouachita mountains to the west, and this, combined with the Mississippi’s turbid character, has served as a barrier to the dispersal of upland fish species between river systems on either side (Robison 1986).

Freshwater habitats

The entire original extent of the Mississippi alluvial plain, stretching 1,120 kilometers from the northern portion of the ecoregion to the confluence with the Gulf of Mexico, occurs here. Swamps, marshes, and other wetland areas, including bottomland forests, were once dominant features throughout this ecoregion. Although these areas still exist in many places, they are not as extensive as in pre-settlement times (U.S. Geological Survey 1996).

Terrestrial habitats

The Lower Mississippi was once dominated by swamps, marshes and bottomland forests, primarily oak-hickory-pine forests (Ricketts et al. 1999). Today, the ecoregion is heavily converted, with just under half of the ecoregion covered by forest. One-third has been converted to agriculture and the remaining areas are comprised of water, wetlands, urban, and barren areas (Smith et al. 2002).

Description of endemic fishes

Only 4% of fish species are endemic to the Lower Mississippi, and these are found in tributary drainages rather than in the Mississippi mainstem. These endemics include a shiner (Notropis rafinesquei), catfish (Noturus hildebrandi),  killifish (Fundulus euryzonus), and a number of darters (Percina aurora, Etheostoma chienense, E. pyrrhogaster, E. raneyi, E. rubrum, E. cervus and E. lynceum).

Justification for delineation

Ecoregion boundaries are taken from Abell et al. (2000) and are based on subregions defined by Maxwell et al. (1995).


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