Late last summer, on August 29th, 2024, the United States Fish and Wildlife Service listed the San Francisco Bay-Delta distinct population segment of longfin smelt (Spirinchus thaleichthys) as ‘endangered’ under the federal Endangered Species Act (ESA). With this decision, the Longfin Smelt joins the Delta Smelt (Hypomesus transpacificus), the longfin’s infamous cousin species, as a list species under the ESA. Longfin smelt had already been listed as ‘threatened’ under the California Endangered Species Act (CESA), but the new federal listing is a sign of the challenges that smelt and the broader Delta ecosystem face. The listing brings additional protections and new regulatory requirements that may further complicate water management in the Delta. This blog post provides an overview of this population of Longfin Smelt, explains what listing means, and then discusses ongoing work at UC Davis and beyond to recover Longfin Smelt populations.