Because of the continuing hot weather and recent cloud cover, pond owners are urged to inspect their ponds on a daily basis (a good practice anytime of the year.) Water temperatures near 90 degrees have recently been reported in a few shallow ponds throughout the area.
Fortunately, the temperature rise has been gradual enough that most fish can adjust to these conditions. However, some mortality of weakened fish is probable. There have been a few reports of dead fish floating in Grundy County ponds and lakes.
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The critical factor right now, however, is oxygen, not temperature. As water warms, its ability to hold oxygen decreases. On the other hand, as the fish’s body temperature rises, they require more oxygen.
To check to see if your fish are undergoing stress due to low oxygen, you need to go out to your pond in the early morning and check for fish swimming with their heads out of the water or gasping in the shallows. A pond’s oxygen level will be lowest just before dawn, because the aquatic plants have not been producing oxygen since the sun went down the night before. On hot, cloudy days, the oxygen level will fall until the sun comes back for the same reason.
If you do see fish struggling for oxygen, a quick response is essential. Add fresh, well aerated water or use some method of agitating the surface water to prevent fish deaths. To oxygenate the water you are adding to the pond, spray it into the air, let it run over a series of baffles or let it splash onto a board before it enters the pond.
Feeding of fish should be reduced or stopped completely until water temperatures return to the low 80’s. Don’t worry, your fish won’t starve, because by now, they have slowed or stopped feeding anyway. Instead, you will prevent the accumulation of additional uneaten food or waste material which reduces the oxygen in the pond as it decomposes.
Treatment of aquatic plants or turbidity is also not recommended until water temperatures drop. The best times to handle these problems are when water temperatures are between 65 and 80 degrees, or when plants are just beginning to grow. If treatments are done right now, no more than 1/5 of the pond should be done at a time with a 14 day interval between treatments. In no way should you do a total pond treatment during hot weather.
Although aquatic plants can be a nuisance to anglers or swimmers, they play a vital role in oxygen production in ponds and lakes. By removing plants now, you not only take away their ability to produce oxygen through photosynthesis, you will also cause the dying plants to use oxygen as they decay. Many times, “pond scum” does not create a problem until it’s time to cool off after a hot day in the hay field. However, if you can live with the algae, do your fish a favor and wait until fall to treat the pond.
Predicted rainfall and cooler weather certainly could help to provide oxygen and reduce the temperatures of area ponds. However, the current hot, dry spell could mean trouble for your fish. Make it a practice to check your pond regularly, so you won’t be surprised by a pond full of “floating” fish.