Climate change imperils upper Mississippi River backwaters. Now nature needs human help.

ALMA, Wisconsin — It's an overcast day in February, and two Wisconsin Department of Natural Resources staffers trek over the ice covering some backwaters of the Mississippi River in Alma.

Using GPS coordinates, they locate the exact spot they visited a few months earlier. 

Jeremy King, a water quality technician, drills a hole through the ice. Then he and water quality specialist Shawn Giblin start taking measurements. 

Fish that winter there, mostly bass and bluegill, generally need the water to be 1° Celsius or warmer to survive. King and Giblin learn the water is colder.

There likely still are fish below the ice, but they are "surviving, not thriving," trying to ride things out until spring, Giblin said. 

The slight temperature variation is a big deal.

It’s an indication of a degraded ecosystem, broken down over time by a changing climate and man-made alterations to the river. If that degradation is to be turned around, nature will need help.

That's where King, Giblin and a host of others come in.

The backwaters are a unique habitat along the upper Mississippi River, protecting fish and wildlife, and allowing them a place to rest, eat and procreate. 

Offshoots of the river’s main channel, the backwaters have little current, kind of like quiet neighborhoods nestled next to a busy highway. They tend to be warmer as well. 

Some fish spend their winters in a particular area of the backwaters that scientists call the Goldilocks Zone. There's enough water flowing in from the main channel that fish can breathe, but not so much that it gets too cold. The zone makes up just 3% to 5% of the total upper river area. 

Climate change having a major impact on the Mississippi River

Climate change is making the backwaters less habitable, and making the Goldilocks Zones inside of them even harder to find. 

Between 2010 and 2020, an almost unprecedented amount of water flowed through the river, blasting cold water into these calmer offshoots. It's as if more cars were exiting that busy highway and entering those quiet neighborhoods at a faster pace, making the streets less safe. The time it takes for the backwaters to “flush,” or for all the cars to leave and be replaced with new cars, has gotten shorter. 

As a result, the fish looking for that just-right habitat to settle in for the winter have found it more difficult to do so.

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Scientists are trying to track these changes to be able to target future habitat restoration projects more precisely to the needs of a given area.

That’s the reason for Giblin and King’s periodic journey down the stretch of the river that forms the border between Wisconsin and Minnesota: measuring how cold and clear the water is and how fast it's moving. 

The disappearing habitat could become an issue for people who fish the backwaters looking for a winter catch, a popular source of recreation for the area. But it's also a broader sign of other climate-induced changes to the ecosystem.

The rate at which the river is changing is worrying

In a 2020 report, Giblin and a DNR co-author wrote that "the backwaters of the Mississippi have suffered some of the most serious degradation as a result of changing climatic conditions," and that there is an "urgency" to address the fate of their habitats.

Years of high water are in part a result of more precipitation, including extreme flooding events, a trend that is expected to continue in decades to come. Between 1929 and 1980, mean annual flow of the river measured at a gauge in Winona, Minn., never exceeded 45,000 cubic feet per second, according to the DNR report. Since 1980, it's exceeded that mark 11 times — six of them since 2011.

More precipitation running over the land and into the water also carries with it more sediment runoff that ends up in the river. It builds up, effectively making the backwaters shallower.

In deeper backwaters, the cold water coming from the main channel stays on top and leaves a warmer zone at the bottom where fish can hang out. But sedimentation is making those areas "increasingly scarce," according to the DNR report, meaning the fish are battling both faster-moving flows and not enough depth to stay warm.

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The Mississippi River, like any river, is bound to change over time. Giblin said it's the rate at which it's changing that's worrying.

And while an uncontrolled river could respond to higher flows and other changes by adapting its surrounding habitat, this part of the Mississippi is governed by a series of locks and dams that control water levels to make it easier to ship goods on the river. Because the dams constrain the river system, it's unable to create new backwater areas that provide more suitable habitat.

The result, especially in backwaters that are flushing especially quickly, is "almost a complete loss of ecosystem," Giblin said.

Habitat projects could fix the problem

If the river can't fix itself, then it's up to humans. The U.S. Army Corps of Engineers, the DNR and its counterpart in Minnesota, and other partners are regularly completing projects to reverse damage, including one planned for the backwaters near Alma in a few years.

Giblin and King's data collection should help pinpoint what changes can be made to renew the habitat as an ideal one for wintering fish. That might end up being as simple as extending a peninsula so it blocks off more of the backwaters from the main river, acting as a shield and speed bump of sorts to slow down water flow.

It's important to know exactly what needs to be done, Giblin said, because money for the projects in each spot is typically a "once in a lifetime" opportunity.

And it's especially important for the fish that need such a specific habitat. Whether a project succeeds or fails can come down to a thousandth of a second's difference in water speed, he said.

Many of the adaptations needed to restore habitat are inexpensive, Giblin said, and would pay off when it comes to protecting the biological diversity that exists in the upper swaths of the river — because the backwater ecosystem is "what makes this part of the river really unique and rich, culturally and recreationally."

Madeline Heim is a Report for America corps reporter who writes about environmental issues in the Mississippi River watershed and across Wisconsin. Contact her at 920-996-7266 or mheim@gannett.com.