The Mississippi River: A Place for Fish

Abstract.—Understanding the ecology of the Mississippi River must begin by recognizing that this 3,371-km long river drains 4.8 million km², about one-eighth of the area of North America.  The vast basin is an inverted triangle extending from the central Rocky Mountains and central Appalachian Mountains south to the Gulf of Mexico.  As such, the river flows through four biomes, seven physiographic regions, and cool temperate to subtropical climates.  In its present, altered state, the river can be ecologically partitioned into headwaters, upper impounded, lower impounded, upper free flowing, and lower free flowing reaches.  Average annual water level fluctuations increase from about 2 m in the impounded reach to 4.5 m in the upper free-flowing reach and 8 m in the lower free-flowing reach.  Seasonally inundated floodplain ranges from less than 3 km² per river km to more than 8 km² per river km.  Except for the 824 km headwaters reach, management is dominated by flood control and navigation.  The river is home to 149 native and 4 introduced resident freshwater fishes with diversity increasing from 60 species in the headwaters to 105 species in the impounded reaches and 120 species in the free-flowing reaches.