The Iowa Department of Natural Resources says they’ve determined a largefish kill in Ventura Marsh near Clear Lake was a natural kill. D-N-R spokesman Marion Conover says low oxygen levels this winter caused a massivefish kill. Conover says most of the fish killed were carp or rough fish. Hesays the kill actually helps because the D-N-R had planned to kill off therough fish in Ventura Marsh.The D-N-R has determined that the fish in Ventura Marsh stir up sediment onthe bottom of the marsh that hampers plant growth. The lack of plant growthcauses an increases in the phosphates that flow from the marsh into ClearLake. Conover says the dead fish in the marsh shouldn’t pose any problems.Conover says the D-N-R will still have to go in and kill the rough fish thatsurvived the winter kill.