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Is it safe to swim in the Mississippi River in the Twin Cities?

A brief primer on current events.

How safe is it to swim in the Mighty Mississippi in the Twin Cities anyway?
How safe is it to swim in the Mighty Mississippi in the Twin Cities anyway?
MinnPost photo by Greta Kaul

If you were a resident of Zürich, in Switzerland, you might take the opportunity on a warm day like this to jump into the cool, clear waters of the Limmat River, which flows out of Lake Zürich. Along the Limmat’s banks are changing rooms and swimming platforms. On hot days, the river is full of people playing in the water.

Because you’re reading MinnPost, you’re likely much closer to the Mississippi, a river nicknamed the “Mighty Muddy,” and better known for dangerous currents and polluted waters than for world-class urban swimming.

Still, if you’ve traipsed the paths along the Mississippi in the Twin Cities or happened by Boom Island in Northeast Minneapolis during the Thursday night waterskiing show, you know people splash around in the river regardless.

If you were a resident of Zürich, in Switzerland, you might take the opportunity on a warm day like this to jump into the cool, clear waters of the Limmat River.
MinnPost photo by Greta Kaul
If you were a resident of Zürich, in Switzerland, you might take the opportunity on a warm day like this to jump into the cool, clear waters of the Limmat River.
How safe is it to swim in the Mighty Mississippi in the Twin Cities anyway?

Current considerations

Minnesotans are no strangers to aquatic recreation: after all, we have more shoreline than California, and our people invented water skis. But many of us tend to spend more of our time recreating on and around lakes — of which there are so, so many — than we do on rivers.

And lakes are a little more straightforward than rivers when it comes to judging safety, because the average lake doesn’t move much compared to the average river. Sure, there are waves when a big speedboat goes by (and Lake Superior is another matter), but there isn’t much in the way of currents, which not only move things — and people — in a river, but change their banks and beds, making them unpredictable over time.

“Maybe there’s a lifeguard [at the lake] and maybe there’s not. Maybe there’s a beach, but the water is still and it might be relatively clear, so you kind of know,” what you’re stepping into, said James Fallon, the data chief for the Minnesota portion of the U.S. Geological Survey’s Upper Midwest Water Science Center.

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Comparatively, the Mississippi is turbid, a scientific way to say the water is cloudy-looking and full of stuff.

“You can’t see down very far and it’s moving, so where you swim in may not be where you come out. And because you can’t see, you really don’t know what’s beneath it, and you might run into something you didn’t know was there,” Fallon said.

The speed of the Mississippi’s currents varies according to the amount of water in the river. When the river is lower, it might move around 2.5 feet per second in the Brooklyn Park stretch. That’s less than 2 miles per hour, but 1 cubic foot of water weighs more than 60 pounds — so there’s still a lot of force moving downstream. If the river were higher, it might move at 4 feet per second —  about 2.7 miles per hour. And the downstream force is stronger. Dive underwater for 10 seconds, and you might end up 40 feet downstream.

Another key consideration is that the river’s flow isn’t uniform: there are dropoffs, obstacles and other factors that change its flow from one step to another across its breadth. And when the water’s moving fast and it’s turbid, you could trip on something unseen in the water and end up in trouble pretty quickly.

chart showing different rates of flow in a cross-section of the Mississippi river
Source: USGS
Current speeds vary across the width of the Mississippi, with deeper sections tending to have faster flows.
Fallon said as he was thinking about the Mississippi swimming safety question, he thought about what the DNR says in winter: that no ice is safe to drive or walk on because it’s not consistent.

“Rivers are kind of that way too. I mean, it’s a relative risk, you need to know the river in the area you’re in and just because it was safe yesterday doesn’t mean it’s safe today,” he said.

Nobody should take the currents in the Mississippi River lightly. Every year, it seems, there are reports of drownings at places where people swim in the river. This month, a 12-year-old boy died in the river near Hidden Falls Regional Park in St. Paul, an area officials say is dangerous because of the Ford Parkway Lock and Dam, a steep underwater dropoff and the curve of the river.

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Pollution problems

Currents aren’t the only safety concern for swimmers in the Mississippi: the water is also less-than-pristine.

The river is much cleaner than it once was: it wasn’t so long ago that sewage from the Twin Cities, animal parts from the stockyards and loads of garbage were routinely dumped in the river. It was seen more as the area’s trash carrier than as a natural asset, and it reportedly smelled terrible.

Efforts to clean up the river since then have been successful, but the Mississippi is still considered “impaired” for recreational use in the Twin Cities area, meaning it has enough harmful pollutants to potentially make people sick.

True, the river begins as a small stream out of Lake Itasca (probably), a couple hundred miles north of the Twin Cities, but it travels and gathers up water full of agricultural and other runoff — like pet waste bacteria that comes in through the stormwater drains that likely line your street.

When the Minnesota Pollution Control Agency measures the impairment of a waterway, it isn’t designed to tell people whether it’s safe to swim today, but rather to give an overall picture of the health of the water, said Pam Anderson, who manages the agency’s surface water monitoring program. The MPCA uses a type of E. coli as an indicator of the river’s impairment for recreational use.

“That variety of E. coli itself isn’t going to make you sick, but when we find E. coli in those elevated levels, it usually means that there’s other bacteria out there in high enough concentrations that you have an increased potential for getting sick if you’re drinking the water,” she said.

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It might seem like the river is safer to swim in after a rain, with a fresh injection of water.

Not so, said Jacques Finlay, a professor at the University of Minnesota’s College of Biological Sciences who studies ecology, evolution and behavior. Storm sewers and other sources of runoff  “are sort of injecting these pulses of pollutants, including pathogens, that could really make you sick. So if you’re catching it at the wrong time, like swimming after a storm, that would probably be especially bad.”

A State of the River report from the Mississippi National River and Recreation Area and Friends of the Mississippi says recreational contact with the river should be limited in impaired sections, and avoided altogether within 48 hours of a rain.

Anderson, at the MPCA, said she and her kids have definitely splashed around in the Mississippi around Hidden Falls and Fort Snelling, but, she emphasized, it’s best to remember that because of the pollution, precautions should be taken when doing so.

“That doesn’t mean you can’t recreate in it, it just means that there’s an elevated amount of bacteria present and so you should just be a little more diligent about making sure that you’re not drinking the water, making sure that you’re rinsing off before and after swimming, those sorts of things,” Anderson said.

Above all, George Stringham, a spokesman for the U.S. Army Corps of Engineers, St. Paul District, said people seeking to swim in the Mississippi should be mindful of the many risks the working river — shared between commercial and recreational uses below St. Paul — presents.

“It’s a shared river … Everyone’s got to be on their toes,” Stringham said.