This essay tracks the two-decade-long struggle to protect the delta smelt and other native fish populations in California. Through the case of the smelt, it asks how the goal of species preservation is integrated into contemporary governmental practice. What values are at play in efforts to sustain the existence of nonhuman life in a setting of intense competition over a diminishing and essential resource? What forms of knowledge are developed to gauge the health of threatened species, and what techniques are used to regulate the provision of water in the name of species protection? The essay suggests that smelt protection efforts are guided by two temporally distinct value orientations. The first is pastoriented, emphasizing the preservation of existing species as a good in itself. The second is future-oriented, focused on staving off an approaching ecological collapse whose onset is signaled by the smelt population’s decline.