page_title: Upper Mississippi River
section_title: Ecology
hierarchical_section_title: Upper Mississippi River / Ecology
caption_attribution_description: English: Lock and dam Upper Mississippi
context_page_description: The Upper Mississippi River is the portion of the Mississippi River upstream of St. Louis, Missouri, United States, at the confluence of its main tributary, the Missouri River.
context_section_description: On the upper reaches near the Minnesota-Wisconsin border, the river's floodplain is between 1.5 and 5 kilometers (between 1 and 3 mi) wide.  South of St. Louis, Missouri, the alluvial floodplain is approximately 80 kilometers (50 mi) wide.  Major tributaries to the Upper Mississippi River include the Missouri, Illinois, Minnesota, St. Croix, Chippewa, Black, Wisconsin, and Kaskaskia Rivers.
  The Upper Mississippi provides habitat for more than 125 fish species and 30 species of freshwater mussels.  Three national wildlife refuges along the river cover a total of 465 square kilometers (285,000 ac).  The largest of them, the Upper Mississippi River National Wildlife and Fish Refuge, is over 420 kilometers (260 mi) long, reaching from the Alma, Wisconsin area down to Rock Island, Illinois. The refuge consists of blufflands, marshes, bottomland forest, islands, channels, backwater lakes and sloughs. It is part of the Mississippi Flyway.
  Although the river is much cleaner than it was in recent decades, water quality is still a priority concern. Agricultural runoff, including sediment, excessive nutrients, (particularly nitrogen and phosphorus), and chemicals from agricultural and industrial sources continue to threaten Upper Mississippi River aquatic resources. In addition new threats continue to emerge such as personal care items including pharmaceuticals and endocrine-disrupting chemicals. The five states bordering the Upper Mississippi River are working together to address water quality issues.
  There is general agreement that nutrients are contributing to the Gulf of Mexico dead zone and to eutrophication problems in Lake Pepin, a large natural riverine lake that is part of Pool 4 of the Upper Mississippi River. National and regional efforts are addressing these problems, but nutrient impairment problems are occurring elsewhere in the Upper Mississippi River as well, particularly in off-channel portions. Excessive nutrients contribute to thick floating mats of filamentous algae or duckweeds that have a pronounced negative impact on light penetration and may threaten the growth and persistence of submerged aquatic vegetation that is important for fish and aquatic life, including waterfowl. Efforts to control nutrients from point and non-point sources in the basin will provide additional benefits.
caption: Lock and dam Upper Mississippi
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