The Iowa Department of Natural Resources is investigating the release of anhydrous ammonia from a chemical plant into the Des Moines River in Webster County. The state agency says technicians at the Koch nitrogen plant near Duncombe discovered the release Tuesday and contacted the D.N.R.

Officials say about 18,000 pounds of ammonia had been released into the river. State officials asked the plant to shut off its wastewater pumps because the ammonia concentrations exceeded its maximum levels allowed. D.N.R specialist Glenn Carper said the plant is now hauling some of the wastewater to Fort Dodge for treatment.

Some will be pumped to another retention pool and recirculated in the plant. The rest of the wastewater will be pumped back and forth between holding pools to aerate it and break the ammonia down.