Enterococcus species are widely used indicators of fecal contamination in recreational waters. For nearly two decades, the Anne Arundel Community College Environmental Center has measured Enterococcus concentrations at dozens of sites along local rivers, providing critical information for assessing swimming safety and overall water quality. This study presents a 17-year retrospective analysis of Enterococcus data collected weekly from May through August. Data were evaluated in three categories: all samples, samples collected during dry conditions, and samples collected following rainfall events of 0.5 inches or greater.
Although significant work has been done to decrease runoff to local rivers as the frequency of storms have increased, long-term trend analysis of Enterococcus concentrations has not been conducted. The findings from this study emphasize the value of consistent, long-term monitoring for accurately identifying trends in water quality. While substantial rainfall events are associated with short-term, localized increases in bacterial concentrations, these spikes have not translated into an overall upward trend across years.
Potential influences on Enterococcus variability beyond rainfall, such as impervious surface and failing septic systems are also considered to provide broader context for observed patterns. Overall, this work highlights the importance of retrospective analyses for informing water quality management decisions and refining public understanding of stormwater impacts on recreational waters.