Pond owners who want to maintain good fishing should be alert for conditions that could lead to summer fish kills, according to the Missouri Department of Conservation.
Vigilance and timely action could save fish's lives.
Conservation Department fisheries biologists say three conditions can cause fish die-offs in ponds: shallow water, excessive aquatic vegetation and too many fish.
In all cases, the ultimate culprit is lack of oxygen.
Ponds should be at least eight feet deep to enable fish to survive hot weather.
Some ponds have ample depth when built, but they lose depth over the years as rains wash sediment from surrounding land. Shallow ponds heat up faster than deep ones, reducing the ability of water to hold oxygen.
So, regardless of how deep your pond once was, it is a good idea to check its depth annually. If the depth is approaching eight feet, dredging could be in order.
Overabundant vegetation also can make things tough for fish.
Plants need oxygen to live, and although they normally produce more oxygen than they use, this condition is reversed on cloudy days. Several cloudy days in a row can cause a die-off of vegetation, and the decay of dead plants saps oxygen from the water.
If the amount of dead vegetation is large enough, fish can suffocate.
If pond owners see fish gulping air at the surface, it is time for action.
One remedy is to spray a fan of water across the surface from a high-pressure hose or mix air and water by running an outboard motor tilted up to produce a "rooster tail" of spray.
Much better, however, is to head off the problem before it occurs.
Remove algae and other excessive vegetation with a rake, and dispose of it below the dam, where nutrients from the decaying plant material will not run back into the pond.
The number of fish in a pond also determines how they are affected by low oxygen levels.
The biggest fish -- those most prized by anglers -- usually are the first to die in summer fish kills.
Anglers can help prevent this problem by taking smaller fish home and eating them.
A Conservation Department biologist can help determine whether your pond's fish population is in balance and offer advice about how to restore balance, if necessary.
For more information, contact a Conservation Department office near you or visit www.missouriconservation.org/n119.