Something Killed 100K Fish in Nevada Marina

State wildlife officials are trying to figure out why all the fish have died in a northern Nevada marina where the stocked fishery has flourished since the man-made lake was created nearly 15 years ago. An estimated 100,000 trout, bass, and catfish have died over the past month in the Sparks Marina along US Interstate 80 east of Reno, apparently the result of a dramatic, unexplained drop in dissolved oxygen levels, says state Department of Wildlife spokesman Chris Healy. And that's "probably a pretty conservative guess," says Healy, who estimates they've stocked close to 1 million adult fish in the lake since 1998.

Scientists say a bitter cold snap could have caused oxygen-poor waters to rise from the old rock quarry's bottom to the surface, but they don't understand what sparked the massive die-off. Fish biologists confirmed that low oxygen levels caused the death of an estimated 3,000 fish in one corner of the lake in mid-December, but they thought at the time that the event was localized and of limited impact. Since then, they've been unable to detect any live fish in the 77-acre lake. "We don't know if any small fish have survived, but for all intents and purposes, the fishery doesn't exist anymore," says Healy. Click for more on the mystery. (More mysterious animal deaths stories.)