See also: Mississippi River

The Upper Mississippi River is the portion of the Mississippi River upstream of Cairo, Illinois. From the headwaters at Lake Itasca, Minnesota, the river flows approximately 2000 kilometers (1250 mi) to Cairo, where it is joined by the Ohio River to form the Lower Mississippi River.

Unlike the Lower Mississippi, the upper river is a series of pools created by a system of 29 locks and dams. The structures were authorized by Congress in the 1930s, and most were completed by 1940. A primary reason for damming the river is to facilitate barge transportation. The dams regulate water levels for the Upper, and play a major part in regulating levels on the Lower Mississippi.

Ecology

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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, Black, 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, bottom-land forest, islands, channels, backwater lakes and sloughs.

Most of the Upper Mississippi River, though, is not clean enough to allow fish consumption or swimming. Fertilizers and animal and human waste have contributed to high levels of nitrogen and phosphorus throughout the river basin. These nutrients initiate a chemical reaction which reduces the amount of oxygen dissolved in the water, which in turn affects a number of riverine species. The phenomenon also contributes to a hypoxic "dead zone" in the Gulf of Mexico.

Navigation

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Navigation locks allow towboats, barges, and other vessels to transit the dams. Approximately 1350 kilometers (850 mi), from the head of navigation near Minneapolis-St. Paul down to Cairo, has been made suitable for commercial navigation with a depth of 2.75 meters (9 ft). The agriculture and barge transportation industries have lobbied in the late 20th and early 21st centuries for a multi-billion dollar project to replace the aging lock and dam system. Some environmental groups and advocates of budgetary restraint argue that the project lacks economic justification.

Each lock & dam complex creates a pool upstream of it. There are 29 locks on the Upper Mississippi maintained by the U.S. Army Corps of Engineers—from Upper St. Anthony Falls upstream to Chain of Rocks downstream. The locks provide a collective 123 meters (404 ft) of lift. Note that there is a Lock 5 as well as a Lock 5A. Note also that there is no Lock 23.

List of pools and locks

	Pool	Locality	Lock	Mile marker	(km)	Distance	(km)
	USAF Pool	Minneapolis MN	Upper St. Anthony Falls Lock	854	1375
	LSAF Pool	Minneapolis MN	Lower St. Anthony Falls Lock	853	1373	1	2
	Pool 1	Minneapolis MN	Lock 1	848	1365	5	8
	Pool 2	Hastings MN	Lock 2	815	1312	33	53
	Pool 3	Welch MN	Lock 3	797	1283	18	29
	Pool 4	Alma WI	Lock 4	753	1212	44	71
	Pool 5	Minnesota City MN	Lock 5	738	1188	15	24
	Pool 5A	Fountain City WI	Lock 5A	728	1172	10	16
	Pool 6	Trampealeau WI	Lock 6	714	1150	14	23
	Pool 7	Lacresent MN	Lock 7	703	1132	11	18
	Pool 8	Genoa WI	Lock 8	679	1093	24	39
	Pool 9	Eastman WI	Lock 9	648	1043	31	50
	Pool 10	Guttenberg IA	Lock 10	615	990	33	53
	Pool 11	Dubuque IA	Lock 11	583	939	32	52
	Pool 12	Bellevue IA	Lock 12	557	897	26	42
	Pool 13	Fulton IL	Lock 13	522	840	35	56
	Pool 14	Pleasant Valley IA	Lock 14	493	794	29	47
	Pool 15	Rock Island IL	Lock 15	483	778	10	16
	Pool 16	Illinois City IL	Lock 16	457	736	26	42
	Pool 17	New Boston IL	Lock 17	437	704	20	32
	Pool 18	Gladstone IL	Lock 18	410	660	27	43
	Pool 19	Keokuk IA	Lock 19	364	586	46	74
	Pool 20	Canton MO	Lock 20	343	552	21	34
	Pool 21	Quincy IL	Lock 21	325	523	18	29
	Pool 22	New London MO	Lock 22	301	485	24	39
	Pool 24	Clarksville MO	Lock 24	273	440	28	45
	Pool 25	Winfield MO	Lock 25	241	388	32	52
	Mel Price Pool	East Alton IL	Melvin Price Lock	201	324	40	64
	Pool 27	Granite City IL	Chain of Rocks Lock	185	298	16	26

References

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Mississippi River