Last month, Nelson Trautman watched his daughter wade in the water in front of him at Humboldt Park beach on Chicago’s Northwest Side.

Behind him, a yellow flag waved atop the lifeguard stand. It indicated city tests found high levels of bacteria in the water — on this day, triple the federal warning level.

“I did not know that,” he said. “But, now that I look at that sign over there, I guess I could have seen that there is a green, yellow, and red system.”

Even if he had read the sign, which simply said a yellow flag can mean “bacteria levels are elevated,” Trautman might not know how risky it is for his daughter to swim in the water. That’s because the same yellow flag can be posted when fecal bacteria, both animal and human, is anywhere from moderately elevated to stratospherically high — and federal rules do not require the city to raise any further alarms.

In fact, Chicago Park District spokeswoman Jessica Maxey-Faulkner said there is no level of fecal bacteria readings that would prompt them to post a red flag or impose a swim ban at a beach.

“We do not have a test number at which we ban,” she wrote to WBEZ in an email. “We ban if there are hazards such as lightning, rough waves, rip currents, or sewage overflow.”

For instance, on Sunday, fecal bacteria at 12th Street Beach skyrocketed to record levels for Chicago beaches — exceeding federal warning levels by nearly 100 times — but the beach was never closed, according to park officials. The levels, however, were posted on the park district’s website.

Trautman was surprised to hear that bacteria levels could be so high without prompting more explicit warnings at the beach.

Samuel Dorevitch, a public health professor at the University of Illinois at Chicago who leads a team that analyzes the beach water every day, thinks the current warning system could be improved.

“Instead of treating all exceedances with the same yellow flag in Chicago, [when levels get extremely high] they could come up some sort of additional warning, something more like a red flag,” he said.

Allison Bartlett, a pediatric infectious disease specialist at the University of Chicago medicine, also advocates for a more nuanced approach.

“I think that there should be some threshold above which the warning about the safety of being in the water is much more strongly worded than the yellow flag,” she said.

Maxey-Faulkner, the park district spokeswoman, noted that the city is following all federal guidelines and has set up a handful of additional ways for the public to get more information.

How do the warnings work?

The park district monitors fecal bacteria in the water by taking water samples every morning. By 1:30 p.m., the readings are posted on the city’s beach website.

The results determine whether the beach gets a green or yellow flag that day.

A green flag means that Enterococci bacteria levels — caused mostly by animal and human feces — are lower than 1,000 calibrator cell equivalents (CCE) per 100 milliliters of water.

A yellow flag means the Enterococci levels are higher than 1,000 CCE, a level associated with 36 gastrointestinal illnesses per 1,000 people who might use the beach that day. This risk of illness is heightened among children, the elderly, and people with compromised immune systems or vulnerability to gastrointestinal illness.

Red flags, according to park officials, are only posted when the beach is subject to dangerous weather conditions or a sewage overflow, such as a storm that causes river backups.

This may be confusing since signs at city beaches say a red flag means “bacteria levels are high.” But Maxey-Faulkner stressed that the red flag is not for the kind of bacteria captured in the daily enterococci sampling.

What warnings are required?

Despite the limitations of the flag system, the park district’s notifications comply with federal guidelines set by U.S. Environmental Protection Agency in 2014. Those guidelines only require municipalities to notify the public if Enterococci are above or below the Beach Action Value of 1,000 CCE.

But do EPA officials believe cities should offer more nuanced advice or actions when fecal bacteria balloons to 10, 20, or even 100 times higher than the agency’s Beach Action Values?

The agency said it’s up to the municipality to establish a level at which they offer additional advice or close a beach.

“There is no further guidance or information [the] EPA provides above those [1,000 CCE] values,” an EPA spokeswoman wrote to WBEZ in a statement. “The public should contact their state or local health department for additional information and advice.”

So what does Chicago’s Health Department advise beachgoers to do when fecal bacteria indicators skyrocket above 1,000 CCE, which has already happened more than 50 times in the last month at beaches including Ohio Street, South Shore, Rogers, 63rd Street, and Calumet?

Health Commissioner Julie Morita’s office offered the following statement:

“CDPH is grateful to have partners in the Chicago Park District who prioritize residents’ health, and conduct monitoring and testing of Chicago’s beaches on a daily basis during the summer season. We recommend following the specific guidelines for each beach that are updated daily on the Chicago Park District website, at each life guard office or via phone message.

The office also sent tips — some more relevant than others — for beachgoers that included “don’t pee or poop in the water,” don’t swallow the water, take kids on bathroom breaks, and reapply sunscreen.

The park district also encourages beachgoers to avoid feeding the birds and to make sure their toddlers are wearing waterproof swim diapers.

Dorevitch, the doctor and UIC public health professor, offered more direct advice for city policymakers.

“I would suggest something like a limited swim ban for children, the elderly, and people with underlying health problems at 10,000 CCE,” he said. “That would be a cautious thing to implement.”

Josh Mogerman, spokesman for the Natural Resources Defense Council, which has researched the issue across the nation, noted that fecal bacteria rates in the Great Lakes are twice as high as coastal waters. And this makes clear messaging around the issue especially important.

“Communication about beach water quality is key,” he said. “They aren’t really protecting public health if the public has no idea what the risks are when they go to the beach.”

What are the health risks?

Calculating the exact risk to Chicago beachgoers is not easy, Dorevitch said. That’s because the 1,000 CCE level was developed by the EPA based on Enterococci from sewage runoff, composed mostly of human waste. Chicago’s particular fecal cocktail, however, is more bird waste than human.

Bird feces, Dorevitch said, is considered less dangerous to humans, but is still risky because it can often contain Campylobacter, a pathogen that can cause diarrhea, fever, and abdominal cramps in humans.

Park district stands by the system

Maxey-Faulkner defended the park district’s notification system and highlighted a variety of ways the public can find the bacteria levels.

“We use a three-tiered flag system, information and notification at beach locations, a beach hotline, a webpage that is updated daily, social media, and media outreach throughout the season,” Maxey-Faulkner said. “There is also a white board at lifeguard offices with information about the sampling and water conditions. We also include a message about risk to vulnerable populations on our phone hotline.”

On Friday, that hotline said: “A swim advisory is issued when levels of bacteria are above the federal water quality standard indicating an increased risk of illness, particularly for small children and those with compromised immune systems. However, should you choose to swim despite the advisory, you will be allowed to do so.”

The park district also directs people to its Facebook page for updates, with advisories that read: “Swim advisory at Humboldt Beach based on water quality. Swimming is allowed but caution is advised.”

One Facebook commenter, clearly confused by the wording, asked: “What does water quality mean?”

It’s also worth noting that on June 10, when 12th Street and 31st Street Beach hit record fecal levels of 67 and 98 times higher than the federal action limit, the park district posted no beach advisories at all on its Facebook page.

What do other cities do?

Although the EPA doesn’t require municipalities to offer much beyond Enterococci readings and notices if they are above or below 1,000 CCE, it does encourage them to offer more context and advice at their own discretion.

In Milwaukee, this includes signs posted on yellow “advisory” days that say: “Swimming in this water could make you sick. Swim at your own risk.” On those days, the city’s beach website further advises, “If you enter the water, take extra precautions: Do not ingest lake water, wash hands before eating, and shower when done swimming. Be aware of other safety hazards associated with swimming, and, as always, swim at your own risk.”

In New York City, officials offer text updates on beach water quality and post signs on beaches that say, “Swimming and Wading are Not Recommended” when fecal bacteria reach advisory levels.

Both Milwaukee and New York close beaches (as Chicago did as late as 2011) when fecal bacteria rise to a certain level — measured through cultured bacteria coliforms of E.coli in a way that is not directly comparable to CCE readings.

Dorevitch, the UIC professor, has done research on the effectiveness of Chicago’s current system, and it did not fare well.

“We did a study … asking people what the yellow flags mean and we found people had a pretty limited understanding of what that meant,” he said. “And we found even messaging people on social media that there is an advisory doesn’t help people if they are not aware what to do when there is an advisory.”

Bartlett, a pediatric infectious disease specialist at the University of Chicago Medicine, said: “Certainly with 1,000 CCE being the threshold for putting out the yellow flag, when you’re 5 and 10 times higher than that — especially in a city where we are blessed to have multiple beaches — I think the best thing is for you and your family to find a different beach where the counts are lower.”

As for Trautman, the father at Humboldt Park Beach, he thinks that something even more basic could help.

“Maybe they could at least put the word bacteria on the yellow flag,” he said. “That way, at least parents would have an idea of why it was flying on the beach.”