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Study: Climate change will make MN fish kills much more likely...and complicated

The cause of one of the biggest MN fish kills this summer remains undetermined, and pinpointing causes could become harder in decades to come.

MINNEAPOLIS — According to the Minnesota Department of Natural Resources (DNR), there are up to 500 fish kills on state lakes and streams every year. According to a new study, that number will increase six-fold by the turn of the century if climate change continues at its current pace.

"We're running out of time," said Simon Tye, a PhD candidate at the University of Arkansas who authored the new study, which combines tens years worth of fish kill data associated with high temperatures and projects them out over future decades according to climate change models.

"It basically represents our expected climate if we continue, business as usual," Tye said. "And what that found is a predicted 600% increase in the amount of events."

"I was very surprised," said Nick Phelps, an associate professor at the University of Minnesota who studies fish health and contributed to the study.

"We knew that, as fish got stressed with warmer water, that number (of fish kills) would go up, but we did not expect it to go up six-fold," Phelps said. "It's projecting, by the end of the century, several thousand fish kills are going to be happening."

Phelps says that is a dire prediction at a time when climate change is already making it harder and harder to keep up, and investigate, fish kills. He says the vast majority of the estimated 500 annual fish kills in Minnesota go unreported.

"Keep in mind, that's only what you're seeing in that spot," Phelps said. "There's likely ten times as many fish that sunk to the bottom of the lake and you're not seeing."

RELATED: Letter to Gov. Walz demands action on fish kills

Phelps says only a fraction of the estimated 500 fish kills that happen here every year are reported at all, and that makes pinpointing their cause tricky.

"You have to get there fast," Phelps said. "The quicker we can get there to try and diagnose it, the better."

Even then, finding a singular answer, or source, of a kill is proving increasingly difficult. One of the largest fish kills reported this summer is a good example. Roughly 2,500 fish, mostly brown trout, were found dead on Upper Rush Creek near Lewiston, Minnesota.

The kill was one of several in recent years that came following heavy rains. Shortly after opening its investigation in July, the Minnesota Pollution Control Agency told KARE11 "Such rainfall events are known to result in contaminated runoff to streams and rivers." 

Weeks later, that investigation remains open.

"People who live in Lewiston said that the whole town had smelled like manure around that time period," said Matthew Sheets, an organizer for the Land Stewardship Project. "We know that some things are happening, but that's also what's happened before and we still didn't get answers then."

Sheets, and other members of the Land Stewardship Project delivered a letter to Governor Walz on Wednesday, asking for more urgency related to the investigation. He says the concerns about runoff pollution in the creek can also impact the aquifer below.

RELATED: Fish kill in Minnesota river tops 2,500; state confirms deaths 'did not occur naturally'

Michael Rafferty, Communications Manager for the Minnesota Pollution Control Agency, provided a statement to KARE 11 in response to the Rush Creek investigation on Wednesday afternoon.

"The Minnesota Pollution Control Agency (MPCA) and Department of Agriculture (MDA) with the Department of Natural Resources (MNDNR) are making concerted efforts to identify the cause of the fish kill in Rush Creek. Results from water quality tests have not provided definitive information as to a specific cause or source. This is often the case because of inherent delays in the discovery of fish kills, reporting, and response. The investigation continues related to manure handling and pesticide use in the 10-square-mile watershed. These types of investigations take time, often months, and when concluded they may not point to a specific cause. Once the investigation has concluded we will provide an update."

Phelps says climate change is a big reason why these investigations have become so complicated and slow. Both warming temperatures, and an increase in extreme rain events, are putting stress on the ecosystem in direct and indirect ways.

"There may be scenarios where a chemical runs off into a river or a lake and the fish might otherwise be able to tolerate it, but now, with other stressors, they'll die," he said.

Though all those compounding factors can be overwhelming, he says it's important to continue reporting potential issues, seeking answers, and taking the steps that we can.

"The future doesn't look great, but I think we have to do something," Phelps said. "Land management practices, preventing the introduction of invasive species, reducing chemical run-off, anything we can do to keep our lakes healthy is going to be good for the fish long term."

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