Fish kills in Ohio ponds and small lakes occur during the summer and winter but they may happen any time during the year.  Fish kills are usually related to low oxygen levels, however, pollution or fish disease and a phenomenon known as turnover can also kill fish.

As water temperature increases, water loses its ability to hold oxygen.  Unfortunately as water warms, the cold blooded fish become more active and require more oxygen.  Aquatic plants are generally considered beneficial to bodies of water because they produce oxygen.  At night and during periods of low light, vegetation actually competes with fish for oxygen.  Decomposing vegetation also requires oxygen, making less available to fish.  Studies show that summer oxygen levels are usually lowest just before sunrise and after extended periods of cloudy weather.

During extremely warm weather, when water temperatures exceed 85 degrees, it's a good idea not to use chemicals to kill vegetation.  If you have to kill vegetation for a special occasion, apply chemicals to no more than one third of the pond and wait 7 to 10 days before you treat the rest of the pond.  Ideally, chemicals should be applied when the water temperature is below 80 degrees.  Adding oxygen by means of aeration is usually easiest on small ponds.  It can be accomplished with a pump and hose, or  running a boat motor in the pond.  Water molecules will pick up oxygen from the air.  So spraying the water in a fine mist works best.  Commercial aeration systems are also available.  Contact the District office for a source of aerators.  Most summer kills run their course within a few days.  If you need a list of fish propagators, contact our office.

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