The DNR’s beach-monitoring system listed “Swimming Not Recommended” advisories for Clear Lake State Park Beach and Big Blue, the city-managed quarry swimming area in Mason City.
The latest posted sample from Clear Lake State Park Beach, collected July 27, showed an E. coli reading of 1,600 most probable number per 100 milliliters of water.
The beach’s five-week geometric mean was listed at 161.6, also exceeding Iowa’s recreational-water standard.
NIT previously reported an elevated E. coli advisory at Clear Lake State Park Beach in June, meaning the popular beach has experienced more than one water-quality warning during the 2026 swimming season.
Big Blue in Mason City was also included among the locally monitored beaches with results indicating swimming was not recommended.
An advisory does not necessarily mean a beach has been legally closed. It means testing found conditions associated with a greater risk of illness, and officials recommend that people avoid swimming until later results show improvement.
Another Northern Iowa warning was posted for Beeds Lake Beach near Hampton in Franklin County.
A July 27 sample from Beeds Lake measured 1,600 for E. coli, while its five-week geometric mean reached 325.54. Both figures were above state standards, resulting in a “Swimming Not Recommended” advisory.
Iowa uses two E. coli standards when evaluating recreational water. The single-sample maximum is 235 organisms per 100 milliliters, while the five-sample geometric mean standard is 126.
The DNR also issues warnings when microcystin, a toxin associated with blue-green algae, exceeds 8 micrograms per liter.
Elevated indicator bacteria do not necessarily mean every person entering the water will become sick. However, they suggest that fecal contamination may have reached the water and that disease-causing bacteria, viruses or parasites could also be present.
Possible illnesses linked to contaminated recreational water include diarrhea, nausea, skin irritation, ear infections, respiratory infections and other ailments.
Children, older adults, people with weakened immune systems and anyone with open cuts or wounds may face a greater risk.
Potential sources of contamination include stormwater runoff, wildlife and waterfowl droppings, livestock manure, leaking septic systems and wastewater problems. Heavy rain can wash contaminants into lakes and beaches and is considered one of the major causes of temporary bacteria spikes in Iowa.
Swimmers are advised to avoid swallowing lake water, stay out of visibly discolored or foul-smelling water and avoid swimming following heavy rainfall.
The DNR normally updates its beach-monitoring website and telephone hotline on Fridays during the recreational season. Conditions can change quickly, and residents should check the latest advisory before traveling to a beach.
Big Blue was always a sacred place. No pollution clean water you could see the bottom at 10 foot or more. So where is the hog shit coming from to make this no swim thing happen ?
And don’t try to blame it on geese…that is completely bull shit.
It’s Biden’s fault.
Wrong. It’s kim Reynolds and the rest of her farmer senators in des Moines that let factory farms ruin our state.
Thought the topic was about Big Blue. l am curious about how it was infected.
They don’t want anyone to know the real reason. God forbid if we blamed agriculture for anything.