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Pond Damage & Renovations

Wave Action:
Many ponds are well protected by simply establishing a good sod growth. The most common method of protection where sod is not sufficient is the use of stone rip-rap. Football sized stones or pieces of broken concrete should be placed along the dam or the affected area several feet above and below the water level. This will effectively protect the area. Another method sometimes used is the placement of logs along the eroded area. Logs are staked at either end and held parallel to shore several feet out in the water. The logs will absorb the energy of waves and prevent erosion.

Muskrat Damage:
Muskrats can be discouraged by removing their food source. Cattails and other vegetation form much of this rodent's food. Mechanical or chemical means can be used to rid a pond of vegetation. They may also be driven from the dam area by placing 1/2 cup of creosote or mothballs in holes drilled at three-foot intervals along the face of the dam near the water's edge. The holes should be sealed shut with dirt after the creosote or mothballs have been added. Muskrats can also be removed by trapping during the trapping season.  Muskrat trapping has provided spending money as well as fun and education for many.

Seepage and Leaks:
The best way to avoid these problems is to use proper dam construction techniques and avoid building a pond in area with exposed limestone or permeable soils. Pond dams with a well compacted clay core tied into existing clay substrate rarely leak providing burrowing animals are not allowed too penetrate the core.  Repair of a leaky dam or pond bottom is often difficult and expensive and requires first draining the pond. A blanket of clay taken nearby or the addition of bentonite to the bottom will seal leaks.

Washout:
One major cause of dam washout is failure to place anti-seep collars several places along the length of the mechanical spillway. These collars prevent water from following the tube, creating a cavity through the dam and leading to dam failure. Another major cause of washout is improper size or placement of the emergency overflow spillway. An emergency spillway that is too small for the flood water going over it will quickly washout the dam. Placement of the spillway on newly placed and compacted soil may also result in a washout during high water. The emergency spillway should be constructed on undisturbed soil.

Muddy Water:
Turbid water in Iowa ponds many times is the result of cattle wading in the pond. Another cause of turbid water is the presence of carp or bullhead. They should be removed by draining or chemical renovation followed by stocking of the proper species of fish. Planting a larger buffer strip around the pond will also act as a filter and will remove much of the silt.

Shoreline Deepening:
Frequently, many future aquatic vegetation problems can be eliminated during pond construction by deepening shoreline areas. Often this could be done at little or no extra cost if borrow areas for dam material are taken from along the shoreline. These areas should be deepened so there is a slope of 3:1 down to a depth of 6 feet. Limit these steep shorelines to two thirds of the pond closet to the dam. Allow the remaining third shallow for fish spawning, nursery areas, and for other wildlife uses.


Renovating the fishery in a farm pond
Fish renovations should be undertaken only in farm ponds with adequate depth (8-12 feet), sufficient size (1/2 acre or larger), controlled watersheds, and undesirable fish populations. Fish population improvements in poor ponds would be short-lived and costly.

Rotenone is a fish toxicant that prevents gill tissue from absorbing dissolved oxygen from the water. It is not toxic to warm blooded mammals at concentrations prescribed for killing fish. Rotenone can be purchased either in powder form or as a liquid. The liquid is recommended because of its ease of application.  Many things about your pond should be known before attempting renovation of fish populations. The pond surface acreage should be determined by visiting you local SCS Office and asking them to measure the area of your pond from aerial photos on file in their office. Average depth is needed to determine the total water volume. Average depth can be calculated by multiplying maximum depth by .4. Multiply average depth times the surface acres to determine volume in acre feet (one acre foot covers one acre one foot deep).

Best results are obtained if the renovation is scheduled in August when water temperature is highest. Liquid rotenone should be used for pond renovation and should be applied at a rate of 3 ppm (parts per million). One gallon of the liquid per one acre equals 3 ppm. Let's say, for example, that you want to renovate your pond to remove an abundance of small bluegills and bullheads. A trip to the NRCS Office and a check of their aerial photographs proves the pond to be 2 acres and a quick test of the depth from a boat using a weighted line shows the depth to be 22 feet. Therefore, to calculate the number of gallons of rotenone you would calculate:

Average depth = .4 x maximum depth or Average depth = .4 x 22 feet = 8.8 feet

Volume = average depth x surface acres or Volume = 8.8 feet x 2 acres = 17.6 acre feet.

Therefore you would need 17.6 gallons of rotenone.

Rotenone can be applied with the use of an outboard motor and boat.  One method is driving around the pond in a boat and pouring rotenone slowly in the water near the outboard. Make more laps over the deeper water than over shallow areas. Continue to mix the rotenone and water with the outboard until all rotenone is applied. In a few minutes, fish will start swimming on the surface and die. Rotenone can be applied by another method, also with a boat and motor. Tie the boat between two steel fence posts in the middle of the dam. Tie the outboard in the center position, start, and run at maximum throttle, in forward gear. Run the outboard for 1/2 to 1 hour, to establish a circulation pattern and begin slowly pouring rotenone in propwash. Continue to mix rotenone and water after all rotenone is applied. Wait for the fish to surface and die.

Allow the pond to detoxify for at least one month before restocking. Rotenone can be purchased in gallon quantities from select DNR fisheries offices. (Note: Rotenone must be applied by a licensed pesticide applicator.) Contact your local district office to find the nearest DNR rotenone source.

Spirit Lake Fisheries Management Office (Northwest) - Spirit Lake, Iowa
Manchester Fisheries Management Office (Northeast) - Manchester, Iowa
Cold Springs Fisheries Management Office (Southwest) - Lewis, Iowa
Lake Darling Fisheries Management Office (Southeast) - Brighton, Iowa

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