Dale Miller, with the ISU Extension Office in Knoxville says that winter fish kills are particularly common in Iowa, especially on ponds with small surface area and shallow water depths. Ice cover reduces oxygen that aquatic organisms can use for respiration. Miller says the best way to avoid fish kills in farm ponds is to add an aeration unit, either an agitator or a diffuser to the pond. He says it’s important to keep at least 2% of the surface open.