Pond water needs to be reasonably clear for production of desirable sight-feeding fish populations. Clear ponds produce several times the amount of fish as turbid ponds. Most ponds will be muddy after a heavy in-flow, but in good ponds silt should settle out within a week. Water clarity should be at least 1 foot or more during most of the year. If the underwater visibility is less than 1 foot, fish production will be decreased due to water turbidity. This amount of clarity is necessary for the production of algae, an important component of the food chain or web. In addition to limiting food production, muddy water can reduce the success of fish reproduction, particularly bass.
To cure the muddy water problem, the source of the turbidity should be identified. An easy way to determine the cause of turbidity is to collect a jar of water from the pond. If the suspended silt settles out within a week and the water above it is fairly clear, the problem is probably due to wind action or the activities of some animals such as livestock, fish like carp or bullheads, or crayfish. If after a week, the water in the jar still remains muddy, the problem is due to the chemistry of the soil type suspended in the water. Often, the problem is a combination of factors.
Muddiness Caused by Soil Type
This is the most difficult muddy water problem to cure. The turbidity is caused by the suspension of clay particles that repel each other and will not clump together to form a particle large enough to settle out. This problem can be treated by adding material which will cause these particles to clump together and settle out.
Agricultural grade gypsum (hydrated calcium sulfate), available from most fertilizer dealers, can clear colloidal clay problems temporarily. It should be scattered evenly over the surface of the pond at 12 pounds per 1,000 cubic feet of water or 525 pounds per acre-foot of water. An acre-foot is 43,560 cubic feet. To calculate the pond’s volume in acre-feet, the surface area of the pond should be measured in square feet and multiplied by the average depth of the pond in feet. This figure is then divided by 43,560. Some ponds built with Natural Resources Conservation Service assistance have acre-feet volumes calculated and on file. If the pond does not clear within four weeks and there is no other source of turbidity, one-quarter the original amount of gypsum should be added.
Another material that can be used to clear clay turbidity is aluminum sulfate (filter alum). This material will cause the clay to flocculate and settle out. An application of about 50 pounds per acre-foot of water will clear most turbid ponds within a week. Alum should be dissolved in water and then quickly sprayed over the entire surface of the pond on a calm day since wave action will break up the floc so it will not settle out. Alum as an acid reaction with the water. If the pond is acidic (low pH) or has very soft water, about 20 pounds of hydrated lime (calcium hydroxide) should first be added per acre-foot of water. Sometimes this liming will cause the clay to settle out.
Organic matter can also be added to water to settle clay particles. This treatment technique is preferred to the addition of gypsum or alum because organic matter increases the pond’s productivity rather than decreasing it. Organic matter provides food for desirable bacteria. As the bacteria break down the organic matter, by-products cause the clay particles to clumptogether and settle out. Manure, weeds, hays, and cottonseed meal will all work. When organic matter decays, oxygen is consumed. Too much organic matter can cause oxygen deficiency in the pond. If organic matter is added, it is best to use something that will decompose rather slowly, such as dry hay. It should be applied at a rate of two small bales per surface acre at 14-day intervals. The bales should be pulled apart and scattered in the shallow water around the pond. No more than 4 or 5 applications should be made per year. Solid bales can also be placed along the shoreline every 40 feet, just into the water.
The above mentioned methods are only temporary measures. These treatments will probably have to be repeated each year (usually at lower application levels) and after periods of heavy water inflow. Ponds with chronic clay turbidity may be best stocked with channel catfish and minnows, in which case treatment of turbidity is unnecessary. Artificial feeding is desirable in turbid ponds because little natural food exists.
Muddiness Due to Wind and Erosion
Strong Kansas winds often cause shoreline erosion and wave action which keep soil particles in suspension. The effect of wind can be minimized by the use of windbreaks and shoreline protection. A standard windbreak can be planted on the upwind side of the pond to dissipate the prevailing summer winds. If the dam is eroding badly, it can be protected with rock riprap or seeded shoreline vegetation. Erosion on the rest of the shoreline can be lessened by deepening the shoreline during construction, thus eliminating mud flats. Eroded shores and/or mud flats on existing ponds can be stabilized by planting a water-tolerant grass such as reed canarygrass or millet. Millet seed can be broadcast over the mud at 10 pounds per acre. Millet grows rapidly to form a dense cover but must be planted each year to maintain a stand.
Muddiness Due to Animal Activity
Livestock having access to a pond will trample shoreline vegetation and wade in the water, especially during the summer. These activities stir mud which can then be carried over the entire pond by wind and wave action. Livestock should be fenced out of a pond if production of fish is important. If livestock water is needed, a pipe through the dam to a tank below the dam will supply it. If this is not possible or feasible, all but a small corner of the pond should be fenced off. This limited livestock access will cause some muddy water, but less than if stock had access to the entire pond.
Fish such as bullheads and carp will cause water to be muddy because of their feeding activities. Removal or control of these species has been described previously.
A dense crayfish population will cause pond water to be muddy due to their burrowing and bottom feeding activities which stir up the bottom mud. The introduction of predatory fish such as largemouth bass or channel catfish will solve this problem. Ponds with a good population of predatory fish will not have crayfish problems.