Using compiled bacterial analyses to predict water quality when certain conditions are observed provides a way to establish a proactive public health policy. In this study, the authors reviewed using the geometric mean various conditions including the amount of rain in previous days, wind direction and speed, tides and high tide height, water temperature, drought or flood conditions for the season, different materials coming into the swimming areas, and the location and amount of any sewage spills. Only three events showed statistical significance (Chi-squared p < .0001): rain events of one inch or more in a 24-hour period under normal weather conditions; rain events over a half inch in a 24-hour period under drought conditions; and when "floatable" material from distant sewage spills (i.e., grease balls) are present at a beach. Such evaluations enable a public health policy to be easily developed that restricts swimming when certain adverse conditions are present without waiting for bacteriological examinations to prove that a problem exists.