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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

August 1998

The Mississippi flows on with renewed natural vigor with the help of man-made habitat improvements. © Jeff Janvrin.

Mississippi River rehab

Restoring the Big River's islands and backwaters for wildlife benefits the human community in unexpected ways.

Jeff Janvrin

The Mississippi flows on with renewed natural vigor with the help of man-made habitat improvements.

© Jeff Janvrin.
Getting to know the river || A breath of air
Rebuilding what's been lost
"If you build it, they will come" || What's next?

How often have you heard the following: "Back in the good ol' days we caught buckets full of fish here, but not now." Or "When I was a boy, we used to see thousands of ducks in this wetland. Now we're lucky to see a single coot." People are concerned about habitat loss in and along rivers, streams and lakes. They want to know what's being done to protect existing habitat or restore what's been lost.

For some good examples, they need look no further than Wisconsin's wet western border.

The Mississippi River has long been the platform for engineering projects large and small. The greatest of these – the system of locks and dams built in the 1930s to provide a minimum nine-foot-deep stairway of water from St. Paul to St. Louis – had an enormous impact on river habitat. Since locks and dams were installed, more than 80 percent of the islands in Pool 8 between Genoa and Stoddard have been lost due to erosion. Some backwater lakes, the preferred home of bluegills, largemouth bass and waterfowl, have filled in at an average rate of a half-inch per year.

While it is impossible to reverse all of the habitat losses on the river, one federal program bears responsibility for restoring and improving Mississippi River fish and wildlife habitat.

Since 1986, the Environmental Management Program (EMP) has provided funding to monitor the Mississippi and Illinois rivers and to restore habitat on these rivers in Minnesota, Wisconsin, Iowa, Illinois and Missouri. The five upper Mississippi River states, U.S. Fish and Wildlife Service, U.S. Geological Survey and three Corps of Engineers districts coordinate habitat projects with the EMP, and citizens are encouraged to share their ideas on projects at public meetings.

Getting to know the river

The methods used to restore or create Mississippi River fish and wildlife habitat along Wisconsin's border depend on where the site is located in a "pool" – the water between each set of locks and dams. (Eleven of 26 pools in the river are located along Wisconsin's border.) Habitat problems change as one travels downstream through a pool.

Each pool essentially has three sections: the upper one-third (the section flowing immediately downstream of a lock-and-dam) looks very much as it did before the locks and dams were built. From the air, this area of a pool reveals the maze of flowing and dead-end channels, shallow water marshes, wetlands and wooded islands that make up the backwaters of the Mississippi River. When the earthen dikes of the locks and dams were built, some of these backwaters were cut off from flowing water. Most habitat projects in the upper third of a pool aim to restore this connection to rejuvenate river currents and help keep oxygen levels high enough for fish to survive during the extreme temperatures of summer and winter.

Lock and dam at Alma, Wis.
The lock and dam at Alma, Wis.

© Don Blegen

Backwater habitat gives way to riverine lakes in the middle third of a pool. Here there will be fewer islands and many more wetlands. Due to higher water elevations, the soils on many islands are too saturated to support trees, so grasses predominate. The Mississippi's powerful current slows down, unable to carry further its burden of silt and sand from tributaries. The result: an unnaturally fast rate of sediment accumulation in backwater lakes.

Habitat projects in the middle section of a pool typically attempt to maintain habitat diversity. Techniques include dredging and altering flows in side channels to oxygenate the backwaters and keep sediment out of sensitive areas.

In the lower third of a pool you'll find numerous islands created where water levels were increased the most by locks. Islands serve many roles in the Mississippi River's complex web of life: deer, raccoons, mink and otters take shelter on them; ducks nest in the lush vegetation; turtles lay their eggs in the golden sand. Islands in the lower third of a pool protect aquatic vegetation by deflecting the current and breaking up waves as they roll across the large expanses of water immediately above the locks and dams. Aquatic vegetation located in the "shadow zone" behind islands is used for food by migrating waterfowl and as shelter by aquatic life.

Erosion has reduced the number and acreage of islands in the lower sections of many Mississippi pools. When an island is lost, a disturbing chain of events begins. River currents now enter the once-protected area, uprooting some of the aquatic vegetation. More vegetation beds are uprooted and lost because of the unchecked energy of waves rolling across miles of open water. The waves continue to build in size, eventually stirring up sediment from the bottom. Once the sediment is suspended in the water, it acts like a liquid veil, shading out light the underwater plants need to grow. Plants die, and valuable habitat is lost. Restoration here is aimed at reconstructing the islands.

A breath of air

The Bertom and McCartney Lakes Habitat Rehabilitation and Enhancement Project, located in the middle section of Pool 11, is an example of a project designed to help bluegills and largemouth bass survive harsh winters. Low levels of dissolved oxygen due to lack of depth, lack of flow and decomposing vegetation occasionally caused fish kills. River managers took a three-pronged approach to enhance fish and wildlife habitat.

The first step was construction of a 1,500-foot channel to improve habitat for current-loving fish (walleye, sauger, smallmouth bass and catfish). By lining the bottom of the channel with six different sizes of rock, managers created freshwater mussel habitat as well. A submerged rock barrier in the channel helped regulate the current and prevent sediment from coming into the backwater.

Next, many backwater pockets were dredged and made deeper, and "connecting channels" were dug from one pocket to the next to provide escape routes for the fish. If oxygen levels became too low in the winter in one of the pockets, the fish could follow a channel to another pocket.

Getting oxygen-rich water into an isolated backwater lake would seem fairly straightforward; just dig deep and let the current flow. But too much current can make the area inhospitable for bluegills and largemouth bass in winter. Recent studies show bluegills will travel two to three miles, and largemouth bass up to 18 miles, to find the right combination of four different conditions for a winter home: Adequate water depth (three feet or deeper), 5 ppm or more of dissolved oxygen in the water, essentially undetectable current, and "warm" water temperatures (32 degrees Fahrenheit or higher).

Over 400,000 cubic yards of silt and clay were removed to create deep-water areas. A 22-acre kidney-shaped island, the project's third feature, was built to hold the dredged sediment and break up waves in McCartney Lake. The island also provided food and shelter for shorebirds, waterfowl and turtles. A unique feature of the project was creating a 10-acre wetland on the island.

Bulldozers pile sand and sculpt islands.
Skilled heavy equipment operators pile sand and sculpt islands. Their designs work with nature so upstream portions are protected and downstream sides flood as the river rises.

© Jeff Janvrin

Rebuilding what's been lost

Some islands are restored simply by building a rock breakwater to protect an area from waves and currents that provides sheltered places for aquatic vegetation to grow. (An example of this island-building technique is the Pool 9 islands habitat project near Ferryville.)

Another island restoration technique uses a bit more human engineering to help nature along. At the Pool 8 Islands Phase One project site, each island begins as a base of sand placed by a hydraulic dredge. Like a huge vacuum cleaner, the dredge sucks up sand and some water into a pipe. The slurry is then pumped through the pipe and deposited on the island site. A bulldozer pushes the sand into a rough configuration of the island's final shape. Next comes a layer of topsoil "borrowed" by a crane and bucket from the river. The finishing touch: planting the islands with a mixture of native vegetation and trees.

To ensure the restored islands do not suffer the same fate as their predecessors, rock riprap was placed along vulnerable sections of the islands' shores. A combination of three other less conventional techniques were used to maximize fish and wildlife benefits and assure the islands will be around for at least 50 years. The first was planting two rows of willows along the shoreline, at a safe distance from the water. This was determined by surveying willow growth on natural islands. Rock groins, the second technique used, stick out perpendicular from the shoreline into the water about 30 feet to capture sand and form a beach. Rock groins have two advantages over riprap: Turtles, shorebirds and other wildlife have access to the water's edge, and building a series of groins is cheaper than rip-rapping an equivalent length of shore.

Third, the design of the islands themselves is perhaps the best erosion-control method of all. By design, a portion of each island's shoreline will gradually be washed away by waves and current to form a beach with a one to 20 slope. This slope was determined by surveying stable natural islands. The islands also are designed so the downstream portions will be flooded first when river levels rise. That way, the entire island chain slowly becomes submerged as the flood waters rise, equalizing water levels on both sides. This feature proved successful during flooding in 1993 and 1997, when portions of the islands were submerged by as much as four feet.

"If you build it, they will come"

The project aims to improve habitat and water quality for a variety of fish and wildlife. We make the assumption that if certain environmental conditions are enhanced, fish and wildlife will "find" and use these improved areas. Determining if a project successfully provided the predicted dissolved oxygen levels, current, temperature, or reduced sediment is fairly easy and can be done shortly after a project is constructed. Determining how fish, wildlife and plants respond to a project is more difficult and takes more time.

Consider Bertom and McCartney Lake. Monitoring immediately showed an improvement in dissolved oxygen and water depths in the area. But a response from the fish populations took six years.

In 1987/88, before the project began, we saw several little fish, but few big fish. This was because the big fish were dying from lack of dissolved oxygen and water depth in the winter. After the project was completed in 1990/91, the fish populations didn't seem to be responding to the improvements. For four years, we saw little change in fish populations.

Then, in 1996, our monitoring began to reveal what was going on. Simply put, once we eliminated many of the limiting factors for a fish's life cycle, we had to give the fish time to do their part. They needed time to grow up, reproduce and repopulate the restored habitat before we could proclaim it a success or failure.

It also takes some time for the river's plants and animals to respond to island projects. Turtle, great blue heron and muskrat tracks on shore are some of the obvious signs wildlife use restored islands. Two island monitoring projects by the Long-Term Resource Monitoring Component of the EMP show that what's underwater is working as well. Use of the islands' "shadow zones" is more extensive than predicted. Aquatic vegetation also appears to be establishing faster in the protected areas of the islands than elsewhere in the lower ends of the pools.

Some projects have far exceeded their predicted benefits. Even the ones that may not have fully met expectations are a success, thanks to what they have taught us. Each new project is built on a base of knowledge gleaned from the successes and shortcomings of those already completed. Monitoring the projects has provided valuable insight into habitat requirements for Mississippi River fish and wildlife, and also has given river managers new tools to aid the Mississippi in creating and sustaining habitat on its own.

What's next?

In 1986 the Environmental Management Program was an experiment. Never before had such a large undertaking of environmental monitoring or restoration been attempted in the world. Today, the EMP is a model for this type of work. Tangible benefits of the program include the wealth of knowledge we have gained about the Mississippi and Illinois rivers, but perhaps the greatest benefit is the hardest to quantify: The EMP has fostered a previously unknown level of cooperation among the state and federal agencies responsible for the river's management.

The first Wisconsin-sponsored project, Lake Onalaska Islands and Dredge Cuts, began construction in 1989. Since then, 17 EMP habitat projects have been built along Wisconsin's portion of the Mississippi River, with 12 more planned for construction before the scheduled end of the program in 2002. In all, more than 50 projects affecting more than 97,000 acres will have been built to restore fish and wildlife habitat along a thousand miles of the Mississippi and Illinois rivers.

Congress is now considering reauthorization of this historic and successful program. The Environmental Management Program got its start through the hard work and support of the people who live near and use the Mississippi River. The future of restoring and protecting the river's fish and wildlife habitat is once again in the hands of the people who care about this great resource.

Jeff Janvrin is a Mississippi River Habitat Specialist with the Mississippi/Lower St. Croix Rivers Team stationed in La Crosse.