Federal health officials also suggest closing beaches for extremely high single readings. For example, the EPA recommends closing a beach if the water has more than 1,000 fecal-bacterial colonies per 100 milliliters of water. Lake Darling's count from the sample taken Monday was the highest in the state at 5,800 colonies. Shinall said Iowa is not using the counts of one type of bacteria, enterococci, for beach advisories. The EPA considers that count the best indicator that harmful organisms are present, but that is based on ocean studies, Shinall said.
Scientists disagree on whether the counts mean as much in freshwater lakes.
Last year, beaches at Beeds and Backbone were closed at times. The other beaches remained open. Beach tests over the past couple of years showed that counts tend to jump sharply when rains of more than an inch fall. They can drop quickly when the sun comes out, killing bacteria.