The public at large is unlikely to rank nutrient pollution among the top threats to water, but excess nutrient levels in national watersheds are a serious concern. The U.S. Environmental Protection Agency (EPA) has labeled nutrient pollution one of the country’s most widespread, costly, and challenging environmental problems, and views it as a major threat to clean water. While the need to reduce nutrient loads in waterways might be clear, the best way to achieve that goal is far from self-evident. In recent years, nutrient trading has emerged as a potential solution to the thorny problem of excess nutrients. As discussed below, trading is potentially well suited to play a significant role in nutrient reduction. However, whether the same is true in the interstate context remains to be seen.