Luke Ellison is holding something most of us will never get to see: a delta smelt. Graceful, iridescent and about as long as my finger, these fish are so rare in the wild that just six adults were found during a sample survey of the Sacramento-San Joaquin Delta last spring. And the Delta is the only place in the world where this endangered species lives – in the wild, that is.

Delta smelt also live in enormous round outdoor tanks and smaller tanks inside dimly lit trailers filled with the sound of running water.