In 2023, the Supreme Court made one of its most devastating rulings in environmental history. By narrowing the legal definition of ‘waters of the United States' (WOTUS), the court opened the floodgates to unregulated pollution. But while tremendously consequential, the decision was also simply the latest in a long series of battles over WOTUS, and which rivers, streams, lakes, ponds, wetlands, and perhaps even farm fields were to be protected by the Clean Water Act of 1972. Waters of the United States is an unprecedented exploration of this history—and its importance for today's efforts to conserve a critical natural resource. The book not only examines how bodies of water are legally defined (and therefore protected), but who gets to decide on these definitions. The result is a fascinating look at the ongoing power struggle between the president and federal agencies, the courts, the states, and Congress, over water quality. Waters of the United States offers the detailed analysis necessary for any lawyer or environmental advocate to understand the nuances of water policy, while spinning a compelling narrative for readers who have never cracked a law book. The unique mix of insights into environmental law, history, and politics is required reading for anyone who cares about the future of the nation's water.