As rain and snowmelt wash chemical pollutants into Minneapolis lakes and the Mississippi River, University of Minnesota researchers are studying how to manage them.

Minneapolis is rich with natural water features, from Minnehaha Falls to the Chain of Lakes and the Mississippi River. The methods of protecting those waters are constantly developing. At the University and its St. Anthony Falls Laboratory, researchers Andy Erickson and Bill Arnold are wrapping up a three-year study that addresses a critical component: stormwater runoff.

Across the United States, stormwater runoff is the largest source of water pollution, Erickson said. As spring rain and snowmelt wash over streets, sidewalks and lawns, they pick up a mix of pollutants, such as fertilizers, pesticides and road salt.

In Minneapolis, runoff is the primary driver behind beach closures, which is partly due to heavy phosphorus levels in the runoff, which create harmful algae blooms, Erickson said. The runoff also carries chemical pollutants into the Mississippi River, which serves as a major drinking water source for the Twin Cities.

Stormwater management is an underappreciated issue, Arnold said.

“People might recognize what they put on their lawns matters, but how integrated that is with our roads and recreational areas isn’t always clear,” Arnold said.

To better understand and reduce stormwater’s environmental impact, Erickson and Arnold have spent the past three years studying how pollutants move through Minneapolis’ stormwater system and how they might be removed before reaching its waters.

Each week, the researchers also analyze samples from the Mississippi River, tracking how chemical levels fluctuate.

“If these chemicals are in high concentrations in the Mississippi, that could have impacts on our drinking water supplies,” Erickson said.

Understanding when pollutant concentrations peak helps drinking water treatment systems adapt.

Their team has also been testing solutions like rain gardens by researching how effectively they filter runoff. Using layers of sand and compost, these systems act much like a household water filter, trapping pollutants and breaking them down. Surprisingly, sand, once thought to be inactive, was able to remove some chemicals, Arnold said.

Minneapolis has changed its ordinances so that the city installs water quality projects as it redevelops streets, said Rachael Crabb, water resources supervisor for the Minneapolis Park and Recreation Board. A recent project along Hennepin Avenue in Uptown included rain gardens, she said.

Projects such as rain gardens are part of a state structural effort called Stormwater Best Management Practices, which include filtration efforts such as stormwater ponds that limit flooding and manage runoff.

“Those practices are all pieces of the puzzle because over time, you need many of these practices to happen to really see a strong effect,” Crabb said.

One example is a project at the Minneapolis Columbia Golf Club, where ponds were added and infrastructure was redesigned to manage stormwater before it flows into the Mississippi River, she said.

Similar efforts are underway across the city, including at the Upper Harbor Terminal and in Bryn Mawr Meadows Park. These projects can have measurable impacts, though they are often gradual, and year-to-year changes can vary widely depending on the weather, Crabb said.

“The commitment to water quality is a forever commitment,” Crabb said. “We are always going to treasure and want to use these water bodies and will constantly need to be doing work to keep our best management practices functioning and look for places for additional practices.”

Stormwater ponds are also a focus of Arnold and Erickson’s work. While some ponds are designed specifically to capture and treat runoff, others are natural ponds that have been connected to the stormwater system.

“We now know that our stormwater practices have a lot of pesticides and tire-derived chemicals in them,” Arnold said. “So we’re contaminating those in ways that we might not want to be.”

One key question remains: What do those pollutants become after they break down, and whether they could eventually reach groundwater, a primary drinking water source for many communities, Erickson said. Understanding this is essential to improving their design.

Looking ahead, the researchers plan to expand their work by studying how stormwater ponds process pollutants, such as whether they act as holding areas or actively degrade chemicals.

As Arnold and Erickson prepare to publish their current work, they look forward to seeing the public’s reaction. Often, it informs their future work as they ask the public and the industry what their concerns are.

In the meantime, protecting waterways starts with individuals, Erickson said.

“What can I do on my property? What can I do with my grass clippings? What can I do with the chemicals I apply, or even the salt on my driveway?” Erickson said. “Those are the ways we can help keep the water clean.”

This story was originally published on Minnesota Daily on April 5, 2026.