Fish exemplify the history of the federal government’s efforts to manage natural resources. Fishing has been a major form of visitor recreation for more than a century and aquatic harvesting by humans stretches back several millennia. It is this long-standing tradition and integration with the parks’ cultural significance that allows the practice of recreational fishing to continue in the parks today. In some cases, it can also contribute to the National Park Service goal of preserving native species. The biological significance of fish to ecosystems makes them an ongoing subject of study and concern. Native cutthroat trout are among the most ecologically important fish of the Greater Yellowstone Ecosystem and highly regarded by anglers. Several factors, exotic species and disease among them, are threatening the persistence of these fish. The National Park Service strives to use the best methods available for addressing these threats, with a focus on direct, aggressive intervention, and welcomed assistance by visiting anglers.