The Department of Ecology says Bellingham's main water supply needs to be cleaned up, or the city needs to find a new source.
The entire city gets its water from Lake Whatcom. Years of use have left the popular lake teeming with pollution and algae.
The department of ecology wants the city and Whatcom County to team up and clean it up.
They are also asking people living on the lake to help out.
Ecology officials will conduct a public review of it clean up plan before submitting it to the EPA.