In April 2014, the Environmental Protection Agency and the Army Corps of Engineers published a proposed rule—“Definition of ‘Waters of the United States’ Under the Clean Water Act”—that defines what waters are covered under the Clean Water Act (CWA). This rule, often referred to as the “Waters of the United States” (WOTUS) rule, could cover almost any type of water, giving the two agencies far greater power than authorized under the CWA. The proposed rule is complicated and vague, with little clarity coming from the agencies. There are four key points that should be known about the proposed rule: (1) it is extremely broad; (2) it is an attack on property rights; (3) it exceeds the broadest interpretation of Supreme Court precedent on CWA jurisdiction; and (4) it was developed through a flawed process. Unless Congress acts, this proposed power grab could soon become a reality—the two agencies recently sent their final rule to the Office of Management and Budget for its approval. Congress should require that the agencies withdraw the rule, and then Congress must define what is meant by “waters of the United States.”