Montana Department of Environmental Quality (DEQ) requested enforcement assistance from the EPA regarding Yellowstone County's failure to apply for a Municipal Separate Storm Sewer System (MS4) discharge permit. Yellowstone County previously maintained permit coverage from 2003 through 2022. Montana DEQ has provided Yellowstone County with a variety of resources to help them achieve permit compliance in the past. The EPA issued an Administrative Order for Compliance requiring Yellowstone County to cease all discharges of storm water to navigable waters, or apply to Montana DEQ for authorization to discharge storm water.