The U.S. Fish & Wildlife Service has delayed for about three weeks a decision on whether to designate the delta smelt, a tiny fish found in the Sacramento-San Joaquin River Delta, as a threatened or endangered species. The decision was scheduled for June 29 but more time is needed for staff reviews of the issue, an Interior Department spokesman said. Environmentalists have asked the government to protect the smelt under the Endangered Species Act, arguing that its population is dwindling because the fish is being sucked up by water pumps and its habitat is being altered by increased demands on delta water. The designation is opposed by state and local officials who fear it would lead to a sharp reduction in the amount of water pumped from the delta. Local agencies that buy and distribute water from the State Water Project have sued to force the Fish & Wildlife Service to turn over internal documents on which the decision will be based.