Olin Feuerbacher couldn’t believe his eyes. It was December of 2017, and he’d been reviewing film captured the night prior, from a captive population of Devils Hole pupfish—the rarest fish on the planet.

These inch-long, electric blue fish have been stranded in a submerged limestone cavern in the Nevadan desert since the last Ice Age. The fish only live upwards of a year, and as such the population is prone to large swings, but lately it’s looked grim: In 2013, the entire population dropped to just 35 fish.

In the years since, the U.S. Fish and Wildlife Service opened the Ash Meadows Fish Conservation Facility, which houses a gigantic, 100,000 gallon replica of Devil’s Hole that can be controlled and protected. The