The U.S. Fish and Wildlife Service pledged in a settlement to reassess its 2009 evaluation.
Jeff Miller, a conservation advocate at the Center for Biological Diversity in San Francisco, is hailing the decision.
"This is welcome news. This is a fish that occurs up and down the West Coast. But the Bay-Delta population is the largest and most significant population of longfin smelt and it's in really bad shape in terms of numbers."
Miller says pumps that distribute Delta water to Central and Southern California are killing the fish. But agricultural groups say cutting back on deliveries will hurt farmers and businesses.
The longfin smelt is a cousin of the delta smelt, which is listed as a threatened species by federal regulators. The fish has been the subject of court battles over delta water pumping. The wildlife service agreed to issue a new decision by September.