The U.S. law that fights water pollution will now apply only to bodies of water large enough for boats to use, and their adjacent wetlands, and will not automatically protect streams, Reuters reports.

Environmental groups said they fear the new policy will muddy the purpose of the federal Clean Water Act and put many smaller bodies of water at risk.

The EPA and the Army Corps of Engineers wrote the new guidelines after the Supreme Court split a year ago in a case about which waters fall under the Clean Water Act.

Because of the split decision, lower courts must decide on a case-by-case basis if the law applies to smaller water areas.