Abstract The Delta Smelt Hypomesus transpacificus is a small translucent fish that lives in the heart of California's water distribution system. It is an endemic species that is on verge of extinction, largely because it is in direct competition with people for water. This article discusses the controversy surrounding this fish by describing (1) the biology of Delta Smelt; (2) California's complex water storage and distribution system; (3) the history of Delta Smelt, including conservation efforts; (4) the present controversies surrounding it; and (5) the future of Delta Smelt. The decline of Delta Smelt is a strong indicator that the ecosystem of the Sacramento–San Joaquin Delta has undergone large-scale changes that make it an unfavorable environment for native fishes. Reversing the trajectory of the Delta Smelt toward extinction will require major shifts in California water policy and water use as well as active management of the smelt's habitat and life history.