Summer weather can be threat to ponds, fish

Friday, July 1, 2016


Mo. Dept. of Conservation

Hot weather, cloudy days, lack of rain, and shallow water could set the stage for disaster in your favorite fishing spot.

Like most creatures, fish require oxygen to live. The amount of oxygen in a body of water will vary with water temperature, aquatic plant densities and amount of sunlight.

As water temperatures increase, water loses its capacity to "hold" oxygen. Unfortunately, as water warms, the cold-blooded fish become more active and require more oxygen. Larger fish of any species are usually the first to die when oxygen concentrations become too low. Fish such as bass, bluegill, channel catfish and grass carp are more susceptible to low oxygen levels than bullheads, carp and other species.

Aquatic plants are generally considered beneficial to bodies of water because they produce oxygen. However, as the amount of sunlight decreases, plants use more oxygen than they produce. At night and during periods of low light, vegetation actually competes with fish for oxygen. Decomposing vegetation also requires oxygen, making less available for fish to utilize. Summer oxygen levels are usually lowest just before sunrise and after extended periods of cloudy weather.

Shallow water also has an adverse effect on oxygen levels. Shallow water warms more quickly and encourages aquatic plant growth, in turn, allowing oxygen levels to be reduced.

Fish swimming near the surface of the water and appearing to be gulping air indicate a low-oxygen problem. In smaller impoundments, a quick response can be the difference between losing or saving the fish.

Because oxygen is in short supply, you must provide it by aerating the water or by adding large quantities of fresh, oxygenated water. Aeration is usually easiest and may be accomplished with a boat motor or a pump and nozzle, using water from the pond itself. Water molecules will pick up oxygen from the air, so redepositing the water in a fine misty spray works best.

Well water can also be used, but because it is also low in oxygen, it must be sprayed onto the pond's surface to be effective. The best solution is always a change in the weather. Cool, sunny days or rain will prevent an oxygen-related fish kill better than anything.

Should chemical control of excessive aquatic vegetation become necessary, avoid treatment when water temperatures are warm, since decaying vegetation will lower oxygen levels even further. As a general rule, apply chemicals to no more than one-third of the vegetation at one time and only when water temperatures are below 80 degrees.

Also, during extremely warm weather, when water temperatures exceed 85 degrees, it's a good idea to reduce or stop feeding fish supplemental foods, because uneaten food sinks to the bottom and decomposes, requiring some of the oxygen that is already in short supply. A healthy pond produces an ample supply of natural foods, so there is no need to worry about the fish going hungry.

Unfortunately, a fish kill only "purges" the body of water of excess fish for a short time and will probably reoccur within a few short years. It is usually a sign of a larger problem, such as poor impoundment construction, lack of watershed maintenance or lack of control on aquatic vegetation.

As always, if you have any more questions, feel free to contact me by email at or by telephone at 573-300-3693.

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