On this humid, hot morning I look outside and see the pond across the road.
If you are a pond owner, you know the joys and the frustration that comes along with it.
Fish kills
Last week I received several calls from landowners concerned about fish kills that occurred within their ponds.
Far too often the immediate response is, “I’m sure it is from runoff from the neighboring farmer applying manure and chemicals to the fields.”
Because I have been involved with the field of agriculture my entire life, I take extreme offense to comments such as these.
If for no other reason than this, I felt it important to explain some basic pond management issues.
Admittingly, agriculture may contribute to certain fish kills, but there are also many other potential reasons for a fish kill. Please do not always assume that it is the farmers fault.
Most fish kills are attributed to one of three major causes: Fish suffocation due to lack of oxygen, poisoning, or disease outbreak.
Unfortunately the only indication there is a problem is a fish kill. Little can be done to reverse a kill once it has started.
Suffocation
For the situations that occurred most recently in our county the fish kills were due to suffocation. These ponds experience an inversion, or sudden thermal turnover.
In both summer and winter, ponds may stratify by temperature. This happens because the water density differs according to the temperature.
Summer stratified ponds are characterized by having very warm surface waters that may be 10-15 degrees warmer than the bottom water.
The surface water usually has enough dissolved oxygen to support fish life. Bottom waters have little or no oxygen because it is being used up by bacteria breaking down organic matter.
This is especially true in heavily vegetated ponds. Once this stratification occurs, any event that causes the oxygen deficient bottom water to mix with the warmer surface water can result in a fish kill.
Mixing of these layers during summer is normally caused by a thunderstorm that produces heavy, cool rain and strong winds.
The rapid inflow of cool surface runoff combined with strong wind and wave action can lead to a turnover (inversion).
Small ponds with large watersheds can be especially susceptible to this.
The most effective way to help prevent this is to install and aeration system to circulate and aerate the bottom water that lacks oxygen.
Chemicals
In addition to a turnover, summer fish kills can also be caused by over-treating a pond with aquatic herbicides.
When chemically treating a pond it is important to know the temperature of the water, the type of vegetation you are trying to control and the volume of water in the pond.
It is strongly suggested to not treat a pond in the hottest part of summer because the dissolved oxygen concentrations will be very low.
In order to reduce the likelihood of a fish kill during this time, no more than one fourth to one third of the pond should be treated at any one time.
It is also recommended to wait about two weeks before applying an additional treatment.
Farm runoff
Fish kills can also be caused by runoff of pesticides, herbicides, fertilizer, petroleum products or by disease.
Proper farm management practices and adequate buffers will help ensure runoff is not a problem. Being aware of the watershed draining to your pond can also help.
I have only touched on a few of the most common pond management problems that occur in our county, but there is much more to proper pond management.
Additional resources
The Ohio Pond Management Handbook is a great resource for all pond owners. Please visit the Ohio Department of Natural Resources, Division of Wildlife and type “Ohio Pond Management Handbook” in the search bar in order to access this document.
Understanding the dynamics of your pond may be very complicated. No two ponds are the same as they vary in age, size, construction, etc.
As with any resource issue, my suggestion is to educate yourself of all potential problems and not be so quick to point the finger.
Many times the finger may need to be pointed no further than at yourself or simply Mother Nature.
