Milk is not appropriate fish food. State officials say employees at an Ankeny HyVee poured 800 gallons of spoiled milk down a storm drain.

The Iowa Department of Natural Resources it’s now working with Hy-Vee to prevent milky water from reaching Fourmile Creek in Ankeny. The DNR’s Ted Petersen says early this morning witnesses started to report that fish were struggling in what looked like white water in a tributary of the creek and, while DNR staff haven’t seen any dead fish yet, but it’s a possibility.

Petersen says bacteria start to break down dairy products once they enter a stream and that reduces oxygen levels in the water.

“When all that oxygen is being used for the breakdown, it doesn’t leave a lot for the fish,” he says, “and that’s when we start to see the fish kills as a result of that.”

HyVee said in a tweet that an employee made an “uninformed decision” in instructing others how to throw away spoiled milk. The milk had spoiled because of power outages from Monday’s derecho.

The company has a contractor working on the cleanup.

(By Katie Peikes, Iowa Public Radio/ Radio Iowa’s O. Kay Henderson also contributed to this story)