Dead gizzards had first started turning up along the shores of Lake Arlington two weeks ago.
The Arlington Heights Park District is working with a water-testing company to determine the cause, but officials believe it was a result of oxygen depletion in the water.
In especially hot weather, “fish kills” — as they are often called — are fairly common in small bodies of water, wildlife experts said.
“Every time people see dead fish they fear the worst and assume chemicals have gotten in the water — that is almost never what happens,” said Dan Stephenson, district fisheries biologist for the Illinois Department of Natural Resources. “Ninety-nine percent of the time it’s a natural thing.”
What usually happens is this: As the water warms up, the oxygen content decreases. At the same time, the fish’s metabolism rate increases, so they need more oxygen. Without enough oxygen, the fish cannot breathe and will die.
“Considering it’s been pretty warm lately and no rain, therefore no influx of more oxygen, that’s probably what it is,” said Jim Robinett, vice president of conservation at the Shedd Aquarium. Source