Clear Lake safe for swimming over the holiday weekend, DNR says

CLEAR LAKE – When summer hits, there’s nothing better than cooling off at one of Iowa’s lakes or beaches. Iowa’s DNR tests the water at beaches weekly so you can enjoy it safely. Beach advisories help beach goers make the best choices about when to swim and when to hold off.  Currently, Clear Lake and McIntosh Woods Beach are marked “safe” for swimmers, but two other Northern Iowa bodies of water – Beeds Lake Beach and Backbone Beach – have advisories against swimming.

What Is Tested?

E. coli is a type of bacteria found in the intestines of people and animals. Most strains are harmless, but its presence in beach water can signal that other, more harmful bacteria, viruses, or other pathogens may be present too. That’s why the Iowa Department of Natural Resources (DNR) monitors E. coli levels weekly throughout the summer.

In addition to E. coli monitoring, the program tracks microcystins. Microcystins are toxins produced by certain types of cyanobacteria (blue-green algae) that often form green, paint-like scums or mats on the surface of warm, nutrient-rich water.These toxins pose health risks but have been a relatively minor issue in recent years, with only 2% to 7% of sampling events resulting in advisories. In 2024, just seven beaches had microcystin-related warnings.

When Does the DNR Issue Advisories?

The DNR tests beach water from Memorial Day to Labor day. It issues advisories when:

E. coli levels exceed safety thresholds:

• 126 CFU/100mL (geometric mean)
• 235 CFU/100mL (single sample)

Microcystin levels exceed safety thresholds:

• 8 micrograms per liter (µg/L)

If levels go beyond these limits, an advisory is posted—not a closure, but a heads-up to use caution.

What Does a Beach Advisory Mean for You?

A beach advisory means the water may carry a higher risk of causing minor illnesses like diarrhea or nausea—especially if you swallow water. If you’re healthy and just wading, you’re likely fine if you rinse off after and wash your hands before eating. But if you have young kids, a weakened immune system, or plan to fully submerge and may ingest water during swimming, you may want to wait until levels drop. Stay out of areas with algae, especially if it has the appearance of oily paint on the surface.

How Risky Is It?

• At around 235 CFU/100ml (CFU = Colony Forming Units), the estimated illness rate is about 36 minor illness per 1,000 swimmers
• As the CFU/100mL results get larger, the potential risk for minor illness goes up, especially for those who swallow water.

Beyond water quality, do you know all the risks?

While the DNR provides information about the quality of the water at beaches, most injuries and fatalities come from drowning.

• Be sure to watch children, know your limits and remember that lake beds are inconsistent and deep holes exist.

• Lifejackets for swimming can save lives! In the spring, it might be warm outside, but the water hasn’t had time to warm up, and cold water can reduce body temperature quickly, drastically increasing the risk of drowning.

The Bottom Line:

Iowa’s lakes offer opportunities for fun and relaxation, but it’s important to stay aware of the potential risks when enjoying the open water. By staying informed about water quality and following safety guidelines, you can help ensure a safe and enjoyable experience. So, get out there and make the most of Iowa’s beautiful lakes—just remember to be safe and take the necessary precautions