The city's park district said the system uses computer software to give real-time predictions based on factors such as as water temperature, modeling of the lake bottom and wave action monitored by buoys.
The previous system required the culturing of daily water samples to check for bacteria, a process that took 18 hours and meant officials would determine whether to close beaches based on data already a day old.
"Closing the beach [based on high bacteria counts] was always frustrating," Cathy Breitenbach, director of lakefront operations for the park district, told the Chicago Tribune. "But this was a frustration that beach managers have had all over the country."
Starting this summer, officials said, beaches would be closed only when sewer overflows have contaminated the water. The rest of the time, real-time data will be posted for would-be swimmers, who can decide whether or not to risk entering the water.
Some experts have questioned the wisdom of leaving the decision to enter the water in the hands of individuals.
"People need to go to the beach armed with the information on what the risks are," said Karen Hobbs, a policy analyst for the National Resources Defense Council. "By leaving it in the hands of the beach-goer, you have to hope they know what to do with that information."