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Alternate Nonnative Fish Control Techniques -- Water management, which <br />utilized an annual cycle of filling and drying of ponds, was investigated as another <br />possible NNFC technique. This technique was not successful at HTSWA where the high <br />water table did not allow annual drying in spite of reshaping a pond to make it shallow. <br />When irrigation water no longer flowed to this pond, the water depth decreased to <br />approximately 2"-3". Given these conditions, winter kill was expected, but did not occur. <br />Water management was successful in another pond located higher in the floodplain <br />where a fall/winter drying cycle eliminated all fish that were present. <br />Another NNFC treatment utilized black plastic (Figure 23). A landowner <br />expressed a desire to remove dense aquatic vegetation and a stunted green sunfish <br />population from his 0.5 surface acre pond without the use of chemicals. To accomplish <br />this, black plastic was laid over the surface of the pond for two weeks in August, the <br />hottest part of the summer. All green sunfish and the aquatic vegetation were <br />successfully removed using this technique. Increased water temperature, reduced <br />oxygen or both may have contributed to the death of the fish. <br />41 <br />Figure 22. Juvenile fathead minnow captured in an endangered fish grow-out pond at <br />Horsethief Canyon State Wildlife Area (Fruita, CO).