DES MOINES, IOWA (AP) -- State officials say an investigation hasn't turned up a cause for a fish kill at a state park in Hardin County in north central Iowa.
The Iowa Department of Natural Resources says thousands of dead fish were reported at Pine Lakes on Sunday. Most of the fish were bluegill and crappie.
Environmental samples were taken, but no contamination was detected and oxygen levels were normal.
Agency spokesman Scott Grummer says the fish appeared to have died before last weekend's heavy rain. He says the rapid rising and falling of the water temperature may have caused a stress in the fish.
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