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.

As many as 100,000 trout, bass and catfish have died over the past month in the Sparks Marina along U.S. Interstate 80 east of Reno, apparently the result of a dramatic, unexplained drop in dissolved oxygen levels, Nevada Department of Wildlife spokesman Chris Healy said Wednesday.

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.

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