Part of the water supply for 25 million Californians and 750,000 acres of farmland has been blocked by a tiny silver fish in the Sacramento-San Francisco Bay Delta. The massive Harvey O. Banks plant pumps in Tracy, Calif., were shut down completely on May 31 to provide protection to a population of juvenile delta smelt, which serve as a “good thermometer for gauging the ecological health of the delta,” says Don Strickland, spokesman for the California Dept. of Water Resources. DWR is not sure when it can resume pumping. Originally, DWR predicted that the pumps would have to be off for only seven to 10 days, but it may take more time, Strickland says. The smelt need to move to more brackish water in the west delta before water pumping can be resumed. Strickland says the state’s water needs are being “managed fine” right now, and there is a supply to tap from Lake Del Valle in the East Bay hills if the smelt make slow progress.