Dr. Billy Higginbotham, Texas A&M AgriLife Extension Service wildlife specialist in Overton, Texas, said landowners with stocked fish ponds should be aware of possible problems with oxygen depletion as hot, still days become more prevalent.

He said between June and September, when the outside air is increasingly hot and pond water temperatures climb, is the time of year when oxygen depletions occur most, for a variety of reasons, such as improper aquatic weed control, too many pounds of fish and the weather.

Higginbotham said typical ponds can sustain 1,000 lb. of fish per surface acre through the summer months. When the environment is optimized and the pond owner stocks heavily, especially channel and blue catfish, and feeds heavily with floating fish rations, the density level easily can be met and exceeded.

Oxygen production via photosynthesis can slow or stop after several hot, still, cloudy days, but fish continue to use oxygen until it falls below three parts per million gallons, which stresses fish, Higginbotham said. Fish will begin swimming to the surface to try to obtain enough oxygen to survive at the air/water interface.

Higginbotham recommends checking the pond at daybreak, when oxygen levels are at their lowest level of the day. The pond owner should act quickly if fish are surfacing for air.

Larger fish are affected by low oxygen levels more than smaller fish, he said. “It’s almost as if they are gasping for air at the air/water interface,” Higginbotham said. “That’s a clear sign of oxygen depletion, and the pond owner should act quickly to avoid a complete die-off of their fish.”

Pond owners can produce more oxygen for fish in various ways.

Backing a boat engine into the pond and circulating the water is one way to create more oxygen, Higginbotham said. Pond owners can also place a water pump in a shallow portion of the pond and spray water along the surface to circulate water along the air/water interface.

Once oxygen levels are restored, Higginbotham said pond owners should investigate the pond conditions that contributed to the depletion. He recommends thinning fish populations to reduce the pounds of fish the pond supports going into the midsummer months, when hot, still cloudy days are prevalent.

Controlling aquatic vegetation can also contribute to oxygen depletion, Higginbotham said. Oxygen is removed from water as plant tissue decomposes, which can create a scenario where a die-off might occur.

Weed control efforts should be done gradually — about 15-20% of the vegetation at a time, and with a week-long break between treatments, he said.

An aeration system is a good investment for landowners to avoid problems or prevent future problems, Higginbotham said.

“Watch very carefully as we enter these still, cloudy days — the dog days of summer,” Higginbotham said. “Be mindful of oxygen depletion and the possibility of losing fish populations.”