Crayfish are important food organisms in the pond. They are on the food lists of birds, mammals, and most species of pond fish. Some species of crayfish may present a problem. These are the burrowers, which make vertical burrows two to six feet deep and pile the mud from their excavation in a "chimney" around the mouth of the burrow. Burrows in moist areas may have connecting tunnels, and in rare cases such tunnels have perforated the dams on ponds. There are currently no effective long-term control methods - cultural, chemical, or mechanical - for controlling these burrowers. High densities of largemouth bass will help keep a crayfish population in check.
Ponds and small lakes are attractive feeding and loafing areas for migrating waterfowl, and more natural-looking ponds may even attract nesting pairs of ducks and geese. In addition, many pond owners may keep domestic ducks and geese. Such waterfowl provide viewing pleasure, and their feeding habits may help to control some weed problems; however, they also can create problems. Coliform bacteria thrive in water enriched with waterfowl droppings, especially when the ducks and geese use the pond year-round. For ponds used for swimming, maintenance of more than one pair of domestic ducks or geese per surface acre of water is discouraged. Domestic ducks or geese are not recommended for ponds used for domestic drinking water supplies.
Several species of fish-eating birds may visit your pond. Large herons and kingfishers appear often on some ponds. If the pond is secluded, the smaller species of herons may even take up residence. Seldom will the small number of fish these birds catch be harmful to your fish population, and seeing them around a pond often provides pleasure to pond owners.
Fish are subject to a variety of maladies, such as grubs or worms, which may be found in or on the skin, attached to gills, or embedded in the flesh. Although aesthetically displeasing, none of these parasites presents a threat to human health provided the fish is thoroughly cooked before it is eaten. There are no practical methods to control these parasites in ponds. One aid to prevent their introduction is to stock the pond using only hatchery-raised fish. Parasites and diseases are prevalent in natural fish populations, and stocking a pond with "wildlings" infected with these organisms could result in their inadvertent introduction into the pond.
Small black spots, resembling ground pepper flakes, are visible in the fish flesh. The life cycle of this parasite includes a fish-eating bird and a snail. Sunfish and minnows are commonly affected.
These parasites appear as small white or yellow spots under the skin and in the fish flesh. Common in many species of fish, they are most noticeable in largemouth bass, bluegill, and catfish. Their life cycles are the same as that of the black grub. Stocking redear sunfish (shellcracker), which will prey upon the snails, is one approach to reducing the prevalence of the infestation.
Most ponds will support a few frogs, which, along with tadpoles, provide another source of food for fish. Many pond owners enjoy seeing frogs, and they enjoy the "music" they provide on warm evenings. Because fish, especially bass, eat both frogs and tadpoles, frogs seldom become overpopulated except in ponds where the bass population has become severely depleted. Management for frogs is seldom successful in ponds that are stocked with predatory fish.
Leeches present in Ohio ponds are usually small (less than one inch long), colorless, and opaque. They are not blood suckers, but feed on decomposing organic matter in the pond. They attach themselves to swimmers, fish, and the legs and feet of ducks and other water birds. Although harmless, leeches can be very frightening and thus detract from the recreational uses of a pond. There is no practical control method that can be recommended.
Muskrats often invade a pond, especially if it is near a creek or a ditch and there are areas of emergent and submerged weeds in the pond for food. Unlike muskrats found in marshes, which build houses from vegetation, muskrats in ponds usually dig a burrow into the bank as a den. Such burrows may present problems, especially if dug into the dam of a pond. If your pond was designed according to NRCS recommendations, the dam should be wide enough that a burrow is not harmful. However, if the dam lacks adequate width or height above water level, a problem may develop. Since muskrats are furbearers and are protected by wildlife laws, the recommended method of control is to trap them heavily during the legal trapping season. As mentioned earlier, large areas of cattails and other aquatic plants also will encourage muskrat activity. Get rid of this vegetation, particularly near the dam, if you expect to reduce muskrat populations. Lining the shoreline with coarse stone (at least six inches in diameter) to a depth of three feet below the water level and two feet above will discourage muskrat burrowing.
Although not common in Ohio ponds, this problem is occasionally reported. Swimmer's itch is caused by a free-swimming parasite that burrows into and irritates the skin of humans. The parasite develops in certain birds and snails before it becomes free-swimming. Elimination of swimmer's itch means controlling the snails. One of the easiest methods of ridding a pond of snails is to stock redear sunfish. Also known as "shellcrackers," one of this species' favorite foods is snails. Redears can also serve as a prey species for largemouth bass and should be stocked with, or in place of, bluegills at the rates mentioned elsewhere in this bulletin.
Turtles of several kinds often take up residence in ponds. Their presence is nothing to be alarmed about, and many people enjoy seeing them. Usually you can spare the few fish they eat, and they may even aid in improving fishing by thinning out some of the small fish. To control turtles, bait turtle hooks (available in bait stores) with raw meat and suspend the hooks under water. Traps can also be built to catch turtles. Most anglers can tell you how to build a turtle trap, or you can contact your county wildlife officer for plans.