SAVING DELTA SMELT

Delta smelt are tiny fish — most adults are less than 3 inches long — and nearly translucent, with a steely-blue sheen on their sides. As larvae, they start out eating microscopic food like unicellular algae, planktonic animals, and small crustaceans. As they grow, their diet shifts almost exclusively to small crustaceans called copepods.

They usually live for just one year, spending their entire existence in the San Francisco Bay-Delta.

Background

Delta smelt happen to be one of the best indicators of environmental conditions in the San Francisco Bay-Delta. This ecologically important estuary is a major hub for California's water system — and an ecosystem that’s now rapidly unraveling. The “smeltdown in the Delta,” as the extinction trajectory of delta smelt is known, has left the once-abundant species in critical condition due to record-high water diversions, increasing water temperature, pollutants, and harmful nonnative species that thrive in the degraded Delta habitat.

This smelt's catastrophic decline is a warning that we may lose other native Delta fish species that have also fallen to alarmingly low levels — including longfin smelt, numerous Central Valley runs of salmon and steelhead, and green and white sturgeon. In fact more than a dozen of the original 29 indigenous Delta fish species have either been eliminated entirely from the estuary or are threatened with extinction.

An analysis in 2006 warned that the delta smelt could go extinct within 20 years, and since then numbers of smelt found during state surveys have been too few to even calculate abundance. From 2018 to 2023, no delta smelt were found. That’s shocking for a fish that was once common in the upper Sacramento-San Joaquin Estuary. Delta smelt probably now exist in the wild only because of emergency hatchery efforts by the UC Davis Fish Conservation and Culture Laboratory.

Our Campaign

Because federal and state agencies are failing to address the ecological problems in the Delta — moving forward with plans for water diversions and storage projects that will increase threats and further degrade Delta habitat — the Center for Biological Diversity is working to ratchet up protections for this species.

A Center petition spurred the California Fish and Game Commission to upgrade the fish’s state protection status from threatened to endangered in 2009. The Center is part of a broad coalition of conservation organizations, fishing groups, and Tribes fighting to stop the proposed Delta Conveyance Project, which would siphon more fresh water from the Sacramento River and Delta and likely drive most of the Central Valley salmon runs to extinction. We’ve filed numerous lawsuits to stop this destructive project, and we’ve also protested the water-rights applications for the Sites Reservoir Project, which would further divert large volumes of water from the Sacramento River to fill a new reservoir. Meanwhile we’re challenging the California Department of Water Resources’ approval of State Water Project long-term operations, which would perpetuate destructive Delta diversions.

The Delta habitat for delta smelt is polluted with often-lethal concentrations of herbicides and pesticides discharged and transported from California's Central Valley into the fish's estuary home. We continue to monitor and oppose harmful chemical pesticide use in California through our Pesticides Reduction campaign.

Check out our press releases to learn more about the Center’s actions for delta smelt.