The fish kill at Lake Ogallala in western Nebraska has been blamed on low oxygen levels in the water.
Over the weekend people reported seeing dozens of dead trout in the lake and canal below Kingsley Dam near Ogallala.
Nebraska Game and Parks Commission biologist Darrol Eichner says the canal water tested out at 2.5 parts per million on Wednesday. Eichner says the fish need at least three parts per million to survive.
Experts say oxygen depletion usually occurs in summer because warm water holds less dissolved oxygen than cool or cold water.