Municipal wastewater discharge permits proposed by the federal government for three northern Idaho municipalities require cutting phosphorus discharges into the Spokane River by more than 90 percent over 10 years.
The U.S. Environmental Protection Agency on Thursday released a draft plan that if approved will require the cities of Coeur d'Alene and Post Falls, and the Hayden Area Regional Sewer Board, to improve treatment facilities to meet tougher standards.
Local officials say the improvements will cost each entity $30 to $40 million.
EPA spokesman Michael Lidgard says the stricter permits comply with the federal Clean Water Act and are intended to protect water quality in Idaho and Washington state.
Phosphorous leads to algae growth and depletes oxygen levels in water, harming fish and causing algae blooms in reservoirs.