The U.S. Supreme Court unanimously ruled Monday that challenges to the Obama-era “Waters of the United States” rule must be filed in federal district courts, as opposed to the federal appeals courts.

The ruling marked the first opinion of the month. Justice Sonia Sotomayor delivered the opinion, which was filled with water puns, though she was not on the bench Monday.

The court heard oral arguments in the case, National Association of Manufacturers v. Department of Defense, in October.

The Supreme Court met to weigh in on which courts had jurisdiction for lawsuits challenging WOTUS, not to decide the merits of the 2015 water rule, which vastly expanded the definition of a waterway that can be regulated by the Environmental Protection Agency and the Army Corps of Engineers.

The definition of a waterway under the rule includes everything from a simple drainage ditch to streams and rivers. That means many more areas would fall under EPA's enforcement jurisdiction and control, from farmers to individual homeowners to oil companies, critics of the rule say.

The National Association of Manufacturers filed a lawsuit challenging WOTUS in federal district courts after agencies promulgated the rule, and the cases were then consolidated and transferred to the U.S. District Court for the 6th Circuit.

The 6th Circuit Court of Appeals in 2016 ruled that appeals courts have jurisdiction over challenges to the water rule.