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 Navigation
Pool
4 is 73 km (44 river miles) long and includes 14,700 ha
(36,300 acres) of aquatic habitat. It is located between Lock and
Dam 3 (above Red Wing, Minnesota) and Lock and Dam 4 (Alma, Wisconsin).
Major tributaries include the Cannon and Vermillion Rivers on the
Minnesota side and the much larger Chippewa River on the Wisconsin
side. Lake Pepin, a riverine lake created by the Chippewa River
delta, is located in the middle of Pool 4. The location of Lake
Pepin divides the rest of the pool into upper Pool 4 and lower Pool
4. The smaller backwaters of upper Pool 4 have been degraded by
sedimentation, whereas the larger backwaters of lower Pool 4 provides
much better habitat for vegetation.
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Pool
8 is 39 km (23 river miles) long and is bounded
by Lock and Dam 7 (Dresbach, Minnesota) to the north and Lock and
Dam 8 (Genoa, Wisconsin) to the south. It encompasses 9,000 ha (22,100
acres) of aquatic habitat. Major tributaries include the Black,
Root, and La Crosse Rivers. The upper section of Pool 8 has high
bank islands adjacent to the main channel, deep secondary channels,
and backwater sloughs. The middle section contains low islands,
braided channels, and small backwater sloughs. The lower section
is a large open expanse of water.
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 Navigation
Pool
13 is 52 km (34 river miles) in length and is bounded
by Lock and Dam 12 (Bellevue, Iowa) to the north and Lock and Dam
13 (Fulton, Illinois) to the south. It encompasses 11,400 ha (28,100
acres) of aquatic habitat. Similar to pools upstream, Pool 13 contains
many high bank islands adjacent to the main channel in the upper
section, braided backwater channels and sloughs in the middle section,
and a large open lake-like area in the lower section of the pool.
Major tributaries include the Apple and Plum Rivers on the Illinois
side and Maquoketa and Elk Rivers on the Iowa side.
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 The
Navigation Pool
26 study area includes water bodies along the Upper
Mississippi River from Lock and Dam 25 (Winfield, Missouri) to Lock
and Dam 26 (Alton, Illinois)–63 km (39 river miles) long–and
the lower Illinois River from its confluence with the Mississippi
River north to Illinois River mile 12. This reach of the two rivers
is bordered by high bluffs on the Illinois side and low elevation
floodplain on the Missouri side. The reach encompasses 9,500 ha
(23,700 acres) of aquatic habitat. Presently, most of the backwaters
of the lower Illinois River are isolated from the river by low levees
so as to decrease sedimentation and allow management for waterfowl.
Likewise, many of the secondary channels of the Mississippi River
are isolated from the river on the upstream side to create backwaters
and to reduce sedimentation.
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 The
Open
River Reach study area in the open river is 84 km
(51 river miles, from river mile 29 to 80) long. The study reach has approximately 7,241 ha
(17,893 acres) of aquatic habitat in the form of open water, sand
and mud flats, and swamps and marsh. The floodplain is extensively
disconnected from the mainstem river by levees. Many of the islands
are now joined to the mainland and most side channels contain closing
structures and become disconnected from the mainstem at moderately
low flows. This river reach is characterized by turbid water, high
water velocities, and sand substrate; thus, the aquatic communities
are dominated by more obligate riverine species than the pooled
portion of the Upper Mississippi River. Major tributaries to the
Open River study area are the Little River Diversion Channel in
Missouri, and the Big Muddy Rivers and Cache River Diversion Channel
in Illinois.
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La Grange Pool on the Illinois River is about 130
km (80 river miles) long and encompasses 10,750 ha (26,500 acres)
of aquatic habitat. It is bounded by Peoria Lock and Dam to the
north and La Grange Lock and Dam to the south. This reach has the
highest proportion of backwaters, except for Pool 4, but these backwaters
are highly degraded by excessive sedimentation over the last 150
years. Many backwaters are isolated by low levees to enhance waterfowl
habitat management. Major tributaries include the Sangmon, Mackinaw,
and LaMoine Rivers.
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