Fall harvest is underway across Iowa, and bare fields with fresh manure could send more nutrients and bacteria into waterways, according to a 2025 Iowa State University study.

The study found that cover crops, or crops planted to prevent runoff and erosion without the intention of harvesting it, cut soil carbon loss from erosion by 68 percent. This means that without cover, all the loose soil and whatever it’s carrying is much more likely to wash into rivers and streams.

The potential of runoff from the harvest follows a 2025 summer in which two thirds of Iowa’s state park beaches went under “swimming not recommended” advisories, following the highest rate of advisories in a decade, according to the Iowa Department of Natural Resources’ beach monitoring program. 

The DNR issued 156 advisories across 39 beaches, ticking up from 145 last year, according to the program. 

Advisories were given weekly over 15 weeks. Advisories consisting of “swimming not recommended” warnings are posted at the beach when E. coli or microcystin bacteria levels are too high, and they are lifted once water tests return to safe levels.

 Daniel Kendall, environmental specialist senior at the DNR, said the advisories came from heavy rainfall that washed fecal matter and sediment into lakes, fueling bacteria spikes. E.coli, a bacterium that can cause impairments and illnesses such as diarrhea and urinary tract infections, was the most notable finding of concern among the lakes.

Kendall said about 26 percent of the weekly samples taken by the DNR triggered advisories, in line with the approximately 26 percent advisory rate in 2010, another heavy rainfall year. 

Kendall said the advisories were not indicative of entire lakes being hazardous, but rather that the beach watershed, or the surrounding land “feeding” the beach water with runoff, is the main issue. 

“If you take the edges of your beach area and you go up the watershed, that watershed is actually pretty small compared to a full lake watershed,” he said. “And so when we’re talking indicator bacteria with our beach sampling, the major contributor to that is what’s within that beach watershed.”

Identifying the specific causes of the bacteria spikes is outside the range of the beach monitoring program, Kendall said. The DNR has another method: Total Maximum Daily Load assessments. 

The assessments investigate streams and lakes on Iowa’s impaired waters list — waters that do not meet state or federal water quality standards for uses like swimming or fishing. They then suggest ways a lake or stream can be modified to meet water quality standards. 

Nine of Iowa’s 40 beaches have been investigated by one of these assessments. Notably, Lake Macbride beach in Johnson County was deemed impaired due to high E. coli levels in 2022. 

By reducing runoff and sediments entering the beach and managing wildlife sources of E. coli, like geese, Lake Macbride was deemed fully supported or acceptable. 

Kendall said the program is in place to make the public aware of bacterial risks, ultimately leaving the choice of swimming up to residents.

“We try to do our best to let people know what these advisories really mean,” Kendall said. “And it’s really tricky on that front, because we’re talking risk, and risk is a hard conversation to have.”

This summer’s beach advisories were worrying but unsurprising to Jen Sinkler, creative director at Progress Iowa, a progressive political advocacy organization.

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“Two thirds of our beaches being closed down is disgusting,” she said. “These hotter summers are leading to more bacteria and algae explosions. If we continue on this path, the practices in place right now won’t  protect us.”

From Memorial Day to Labor Day, she, along with other volunteers called on by Progress Iowa and Driftless Water Defenders, signed up to go out to Iowa’s bodies of water and record their findings with the 48 lakes hashtag.

Sinkler signed up to monitor Diamond Lake and said she found an alarming number of algae clusters. She pointed to the state’s concentrated animal feeding operations and nitrates used in farming as the principal cause of the algae and bacteria problem.

 “One thing everybody can agree on is we don’t want to be sick, we don’t want to die, we don’t want our families to be unhealthy, and policy needs to match that, “ Sinkler said.

She cited the fact that Iowa contributes approximately 55 percent of the nitrate load to the Mississippi River Basin, claiming that Iowa’s negative impact through agricultural runoff is often unnoticed.

“Iowa is overlooked in a way that is dangerous,” she said. “We are incredibly powerful, and we can use our powers for good or with a lot of really dire consequences. Right now, our agricultural practices aren’t only making us sick, but they are making us the sickest in the nation.”

Matt Lancaster, an Iowa City resident who graduated from the University of Iowa in 2007, swam at Lake Macbride several times over the summer. The lake had three advisories this year, including one over Labor Day weekend. Last year, it had none. Lancaster said he has swam in Iowa’s bodies of water without a second thought all his life. 

“I’ve never even really thought much of it until the past year,” he said. “It’s ignorant on my part, especially considering that my dad passed from pancreatic cancer in 2022, my mom is currently battling breast cancer, and my mom’s two sisters have both passed from cancer in the last four years.”

Lancaster used to live in Le Mars, Iowa, where he suspects packed hog barns could have made his childhood lakes unsafe with bacteria from manure. 

Both of Lancaster’s grandfathers died of lung cancer. He suspects the water quality could be correlated and hopes to see more research afforded to Iowa’s water quality and the effects runoff has on its residents, believing that the issue has become too caught up in party politics.

“The fact that we have to fight so hard for water testing and research to find causation on the growing cancer rates is not only extremely irresponsible but also is a deliberate attack on our literal survival,” he said.