Nonpoint source pollution is “the leading remaining cause of water quality problems” in the country. Approximately “half of all water pollution” choking our rivers comes from nonpoint sources, degrading at least “80,000 miles of rivers and streams” and “2.5 million acres of lakes and reservoirs.” Though states may disagree on the proper degree of regulation that pollution requires, water pollution does not stop at state borders; loosely regulated states still impair their neighbors’ water quality. The federal common law of nuisance can help address the nonpoint source pollution problem. By reviving this tort, the states would regain a powerful tool to defend their environments from out-of-state harm.