| Summary: | A study was conducted at Acacia Beach, Canyon Lake, Arizona, to clarify the influence of sediment-stored fecal bacteria on swimming area water quality. An additional goal was to determine the value and potential applications of fecal coliform analyses of bottom sediments for use in sanitary evaluations of natural swimming areas. Concentrations of fecal coliform in sediment were found to be significantly higher during the swimming season than during the nonswimming season. Analyses frequently found large, unpredictable changes in sedimentary fecal coliform concentrations over short time periods. Fecal coliform concentrations in near-shore sediment at Acacia Beach are apparently strongly influenced by currents, wave action and sediment agitation by bathers. Methods of analysis used in this study were not able to quantitatively determine the influence of sediment-stored bacteria on the overlying water at Acacia Beach. Use of fecal coliform analyses of bottom sediments as a stable index of overlying water quality or as a predictive device cannot be made from information collected in this study. However, sediment sampling to supplement routine water sampling is recommended to provide a more complete indication of the total sanitary condition of natural swimming areas.
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