The U.S. Environmental Protection Agency has threatened to take over protection of Iowa’s waterways from the state.

A federal investigation shows the state has been lax in requiring that livestock operations follow rules to keep manure out of Iowa’s creeks and rivers, ponds and lakes.

The EPA report says the state hasn’t properly inspected livestock facilities and failed in its duties about half the time when responding to livestock pollution.

According to the Des Moines Register, the investigation was prompted by a petition from environmental groups.

The Iowa Natural Resources Department says the EPA criticism is misplaced.

DNR spokesman Kevin Baskins says his agency has been encouraging compliance, rather than imposing fines and other penalties as punishment for failure to follow environmental rules. And Baskins says there’s evidence the strategy is working.