The U.S. EPA has neglected to pursue hundreds of potential violations of the Clean Water Act because of regulatory uncertainty, according to an internal memo. The lack of clarity stems from a 2006 Supreme Court ruling that left plenty up in the air about the types of waterways and wetlands that fall under EPA jurisdiction. The confusion has had “a significant impact on enforcement,” wrote an EPA enforcement and compliance official in a March memo to the agency’s assistant administrator for water. From July 2006 to December 2007, said the memo, the EPA failed to pursue 304 cases that would have clearly violated the Clean Water Act before the court’s ruling. The agency also chose to “lower the priority” of 147 other cases. The memo was released Monday by Reps. Jim Oberstar (D-Minn.) and Henry Waxman (D-Calif.), who stated that they have “grave concerns over the current status of implementation of the Clean Water Act” and asked that the EPA provide information about its enforcement process.