State investigates fish kill in Ankeny after Hy-Vee workers dump milk down sewer

State investigators are assessing a fish kill in an Ankeny stream that feeds Des Moines’ water supply after Hy-Vee workers dumped 800 gallons of milk down a storm sewer. 

A worker at the Hy-Vee in northern Ankeny told crew members to pour the milk in a storm sewer that dumps into a tributary of Fourmile Creek, Hy-Vee spokeswoman Tina Potthoff said in an interview. Fourmile discharges into the Des Moines River, a major drinking water source for 500,000 central Iowa homes and businesses.

The workers will be required to take Iowa Department of Natural Resources training on proper disposal methods after the isolated incident, she added. Potthoff said the dumping didn’t reflect Hy-Vee’s environmental policies. 

The incident was Tuesday night, and by noon Thursday, the state started finding dead minnows and small game fish in a tributary to Fourmile, DNR reported. The milky water had not reached Fourmile Creek.

“It’s important to know that storm drains flow underground directly into a nearby stream,” DNR supervisor Ted Petersen said in a statement. 

The store is at 410 N. Ankeny Boulevard.

Hy-Vee hired an environmental services contractor to install small dams and pump contaminated water, Potthoff said.

When bacteria break down milk and other organic material in a river, they consume oxygen, often leading to a fish kill. 

State fisheries workers plan to estimate the extent of the fish kill Thursday. The state will consider “appropriate enforcement action,” possibly including a charge to replace the fish, DNR reported. 

Potthoff said Hy-Vee has agreed to pay the cost of the investigation and cleanup, and would be willing to discuss fish restitution.

“We want to be a good community partner,” she added.

The state tracks fish kills, which often are caused by hot conditions, fertilizer and chemical spills, and runoff pollution.