A new aquatic invader, the golden mussel, has penetrated California’s ecologically fragile Sacramento-San Joaquin Delta, the West Coast’s largest tidal estuary and the hub of the state’s vast water export system. While state officials say they’re working to keep this latest invasive species in check, they concede it may be a nearly impossible task: The golden mussel is in the Golden State to stay – and it is likely to spread.

In the vast labyrinth of the West Coast’s largest freshwater tidal estuary, one native fish species has never been so rare. Once uncountably numerous, the Delta smelt was placed on state and federal endangered species lists in 1993, stopped appearing in most annual sampling surveys in 2016, and is now, for all practical purposes, extinct in the wild. At least, it was.

Bruce Babbitt, the former Arizona governor and secretary of the Interior, has been a thoughtful, provocative and sometimes forceful voice in some of the most high-profile water conflicts over the last 40 years, including groundwater management in Arizona and the reduction of California’s take of the Colorado River. In 2016, former California Gov. Jerry Brown named Babbitt as a special adviser to work on matters relating to the Sacramento-San Joaquin Delta and the Delta tunnels plan.