The United States Fish & Wildlife Service Monday officially listed the longfin smelt as endangered. … In the San Francisco Bay-Delta region, [the longfin smelt] is restricted to the San Francisco Bay estuary and adjacent areas of the Pacific Ocean. The endangered Delta smelt — listed so a number of years ago by the state — is a 3-inch fish found only in the Sacramento-San Joaquin Delta.  … [The Delta smelt] is one of the reasons why large southwest San Joaquin Valley agricultural interest and urban water users in Southern California are pushing for the $20 billion Tunnel project. It is unclear if the latest listing under the federal Endangered Species Act of the longfin Bay-Delta Smelt will impact the tunnel project that would divert water out of the Sacramento River before it reaches the Delta. That said, the water diversion — coupled with this week’s federal order — could ultimately impact how water is managed to protect the Bay-Delta smelt in addition to what is already in place for the Delta smelt.