In moves that environmental advocates fear will punch holes in the Clean Water Act,  the Supreme Court has issued rulings that have “left it uncertain which waterways are protected by the law,” according to the New York Times.

Environmental Protection Agency regulators say as things stand now, they may be unable to prosecute about half of the country’s known water polluters because of a lack of clear jurisdiction. The Supreme Court’s rulings interpreted the “navigable waters” language in the Clean Water Act in ways that lawyers say have created uncertainty about which rivers are subject to the law, opening the door for polluters to claim their activities are not covered by the act.

“We are, in essence, shutting down our Clean Water programs in some states,” Douglas F. Mundrick, an E.P.A. lawyer in Atlanta, told the New York Times. “This is a huge step backward.”

Not only could this legal limbo affect watersheds that provide drinking water, it may also affect the headwaters of rivers that empty into the Chesapeake Bay.

Citing EPA reports, the NYT reported that some 117 million Americans get their drinking water from sources fed by waters that are vulnerable to exclusion from the Clean Water Act, based on these cases decided by the Supreme Court.