Thursday May 28, 2026
Maven’s Notebook —
Delta smelt are a small open-water fish found only in the San Francisco Estuary. The species was listed under the federal and state Endangered Species Acts in 1993 and 2009. As populations have continued to plummet, it has become a major focus of California water management.
Studies in the early 2000s showed that summer and fall are especially difficult periods for Delta smelt and that the amount of suitable fall habitat had declined. Those findings led to management actions aimed at improving conditions during this critical period.
In 2008, the biological opinion for State Water Project and Central Valley Project operations required the Department of Water Resources and the U.S. Bureau of Reclamation to keep Fall X2—where salt concentration is 2 parts per thousand—at 74 km or less from the Golden Gate in September and October of Above Normal and Wet years. updated permits issued by the U.S. Fish and Wildlife Service and CDFW in 2019 and 2020 changed the Fall X2 standard to 80 km and added operation of the Suisun Marsh Salinity Control Gates to move freshwater from the Sacramento River into Montezuma Slough.