How Chicago Got a Lot Faster at Beach Water Warnings

Millions of people in the U.S. get sick every year (often with a gastrointestinal illness) after swimming, boating, or fishing at a beach. Not that cities and states with beaches don’t try to prevent this. Authorities measure fecal bacteria—from sewage, birds, or other animals—in the water as an indicator of what other illness-causing organisms might have been released with the waste. If the levels are too high, they post a warning.

Under the usual method, labs grow bacteria from water samples, a process that takes about 24 hours to show results. So by the time high pathogen levels are evident and a beach warning goes out, “Mom is picking up the baby, washing sand out of their pants, and getting into the car,” said John Griffith, a principal scientist with the Southern California Coastal Water Research Project.