DNR says high water causes Mississippi River fish kills - WXOW News 19 La Crosse, WI – News, Weather and Sports |

DNR says high water causes Mississippi River fish kills

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Reports of hundreds of fish found dead in the Mississippi River had the local DNR agencies investigating the cause. 

Earlier this month, biologists with the Minnesota and Wisconsin DNR were contacted by a local marina concerned about the fish population in their area.

Kim Benson, owner of Lawrence Lake Marina in Brownsville said fisherman started notifying him about two weeks about of dead fish sightings. At first he wasn't too concerned, but when they were seeing hundreds, he called the DNR.

"They were concerned because they are not used to seeing something like that at all. Maybe a dead fish here or there but certainly not groups of dead fish," Benson said.

Within an hour DNR biologists were out on the marina investigating. They took water samples and tested the oxygen levels. 

"Usually if it's one or two fish we won't follow up on it but if we get to what we call a moderate fish kill level where you have a 100 to 150 to 200 fish we'll start to follow up on it," Shawn Giblin, Mississippi River Water Quality Specialist with the Wisconsin DNR said.

Giblin said high water played a role in the deaths. 

"Basically how these back waters work is when the river comes up it will push a lot of water into these back waters and then the river came down relatively rapidly so all that organic material up in those wetlands basically moved out of these back water complexes very quickly and that depleted the oxygen," he said.

It takes oxygen to break down the organic matter moving out of the wetlands and without it, the fish can't survive. 

Also, with the high summer temperature hot water can hold less oxygen and can speed up the decay of vegetation, a process that consumes oxygen. The recent rains caused the low oxygen water to be flushed out into other parts of the river causing the death of the fish that were unable to escape quickly.

But the DNR said you can play a role in reducing the damage. 

"We can do things in our own backyard to help the water infiltrate into the ground rather than deliver to the river really rapidly. Things like rain barrels, rain guards, storm water retention bases, stream buffers. There's certainly things we can do to reduce the extent of these kills," Giblin said.

Lawrence Lake was not the only spot that saw these fish kills. Pools 7 and 8 had reports of them too. The DNR said as water levels get back to normal, the low oxygen levels are improving, however it is still possible that other ares of the river will be affected.

If you see large numbers of dead fish in an area, contact the DNR office at 800-422-0798. A state officer is available 24/7. 

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