In the Furrow
Monitor Ponds for Oxygen Depletion
By Will Duffie County Extension Coordinator

Oxygen depletion is the most common cause of fish kills in ponds. Several ponds have already

experienced this troubling situation in Burke County this August. It can occur from April through November, but is most common in July, August and September. The hot weather during these critical months can trigger oxygen depletion.

As ponds lose water, the fish become more crowded and stressed because they are confined in a smaller volume of water. Adding to this stress is the deterioration of water quality as water evaporates from the pond. As fish and other aquatic organisms are crowded into an increasingly smaller volume of water, the less the total amount of oxygen there is for fish to breathe. Adding insult to injury, the warmer the water, the less dissolved oxygen it can hold.

The best solution for most pond owners is to refill the pond. Otherwise, be prepared to treat the pond for oxygen depletion. The most effective treatment is mechanical aeration of the water. There are a number of ways the water can be aerated mechanically. Whichever method is used, the sooner it is applied and the larger the volume of water sprayed or agitated the better. If mechanical aeration is used, it is important not to disturb the bottom mud. Bottom mud contains a large amount of organic material and decomposing bacteria that will contribute to oxygen depletion problems if mixed with water. If mechanical aerators cannot be used continuously, they should at least be operated during the hours before sunrise.

Bushhog mowers can also be used to aerate a pond. Essentially, they are backed into the water and the mower blade is used to circulate the water. Outboard motors also produce a current if used in a fixed position. However, driving a boat in the pond in order to stir the water is practically useless. Be extremely careful when using equipment in a pond. Chemical measures can also be used in the emergency treatment of a pond.

During the critical months, be aware of local weather conditions and look at your pond frequently. There are several signs of a developing oxygen problem: (1) fish swim at the surface and gulp; (2) fish stop feeding; (3) rapid change of water color from bright green to brown.

Oxygen is at the lowest daily level at dawn. If oxygen has not depleted to a lethal level, fish are at the surface early in the morning but return to deeper water as oxygen builds up during the day. This may occur several days before fish begin to die. Check a pond at dawn. If signs of oxygen depletion occur, take immediate corrective action.

For more information contact the UGA - Burke County Extension Office at (706) 554- 2119.