At the North Avenue Beach on Friday, Marissa Fetter’s three children got an early start on the holiday weekend. She visits this neighborhood beach at least once a week during the summer.

“They love it,” Fetter said. “It’s close, it’s convenience and it’s a free outing.”

But she worries about seeing red flags on the beach that mean Lake Michigan’s water is not safe to swim in. 

The city says the beaches will see anywhere from 7 to 9 million people during the summer season, which begins Memorial Day weekend and ends on Sept. 5. 

Since 2011, the City of Chicago has used an algorithm to predict E. coli levels at beaches. The city uses that information to issue swim warnings or bans.

Chicago web developer Scott Beslow started a website last year called Drek Beach, which tracked those warnings and compared them to the measured level of E. coli at beaches. He found that often the city predictions were off.

After Beslow brought the information to the city, they agreed to work with him and volunteers at the Open Government Hack Night to improve its methods. 

Cathy Breitenbach, director of cultural and natural resources for the Chicago Park District, said the city is hopeful the collaboration could improve the process.

“We’ve got all this data, and we have a problem we need to solve and there’s people out there who were interested in bringing their own expertise to help solve it,” Breitenbach said. “If it turns out they can improve upon the models we’ve built, we’d be very happy to see how we can implement it.”

For people who’ve already taken the plunge to swim, there are other safety challenges.

Eric Fisher manages the beaches and pools for the Chicago Park District. He says the biggest challenge is to get people to swim within a lifeguard’s line of sight.

“We try to move our staff around and sometimes you see the patrons want to swim somewhere else when the lifeguards come closer,” Fisher said.

Yolanda Perdomo is a WBEZ reporter. Follow her @yolandanews. Chris Hagan is a WBEZ digital producer. Follow him at @chrishagan.