New York City, the District of Columbia, and 15 states filed a suit against the Environmental Protection Agency (EPA) on Monday, claiming that the rollback of protections for US waterways is “arbitrary, capricious, not in accordance with law, and without observance of procedure required by law.” The rollback came via a change in the definition of protected waters in the United States. Unprotected waters could be threatened by pollutant discharge.

In October, the EPA redefined “waters of the United States” as mentioned in the Clean Waters Act. Before October, the EPA adopted the definition that “waters of the United States” referred to traditionally navigable waters, as well as not navigable waters if they affect the integrity of the navigable waters of the United States. The new definition does not include waters that affect the integrity of navigable waters, instead including only navigable waters.

The states claim that the change in definition defies the fundamental purpose of the Clean Water Act which is to “restore and maintain the chemical, physical, and biological integrity of the Nation’s waters.” Further, “[the EPA] did not explain how they would interpret ‘waters of the United States’ based on training and experience.”