Public Health Risks Associated with Escherichia coli and Cyanotoxins in Urban Lakes: A Case Study from Richmond, Virginia

Lakes are an integral part of urban landscapes providing ecological, recreational, and public health benefits. These lakes are typically located in densely populated areas and subject to urban influences on water quality. Nutrient inputs promote algal blooms that may include toxic forms, while harmful bacteria (Escherichia coli) are introduced through stormwater runoff and sewage overflow events. We monitored nine lakes in the Richmond area to assess potential public health threats associated with the presence of algal toxins (microcystin) and E. coli. The lakes were sampled every 3–4 weeks during May–October 2025 to assess seasonal patterns and inter-lake differences. Overall, 46% of the 72 samples had E. coli concentrations at, or above, recreational safety thresholds. The highest E. coli concentrations were observed following rainfall events when 78–100% of samples exceeded safety thresholds. Rainfall during the preceding 72 h was found to be a significant predictor of lake E. coli concentrations (R2 = 0.43, p < 0.001). Chlorophyll-a varied widely, both among lakes and seasonally, though microcystin remained below recreational safety levels in undisturbed samples. Elevated levels of chlorophyll-a and microcystin were found in samples collected following sediment re-suspension, as might occur during near-shore recreational activities, indicating that benthic algae may be an important source of algal toxins in these lakes. Overall, the results indicate that E. coli poses the most immediate public health concern in these urban lakes, but disturbance effects on benthic algal communities may be an important vector of exposure to algal toxins. These findings underscore the importance of regular monitoring to identify and mitigate water quality issues in urban waters to protect community health.