Effect of Rainfall Events on the Microbial Quality of Recreational Water in the Swan and Canning Rivers in Western Australia

Abstract

Background: Rainfall events are known to be associated with the health of recreational water. Pathogens in recreational water may pose a risk to bathers and water users, including naturally occurring microorganisms as well as those that are present as a result of faecal pollution. This study aims to investigate whether rainfall events impact on the microbial quality of recreational water in Swan Canning estuary in Western Australia (WA) and to identify and propose effective management interventions. Methods: Compliance of water quality in recreational waters is assessed according to microbial water quality assessment categories (MACs) based on the 95th percentile of enterococci counts with the use of Enterotester TemplateTM. Results: Results indicate that the number of enterococci in the water rises along with increasing volumes of rainfall. Enterococci levels between 201 to 500 MPN/100ml are associated with rainfall ranging from 3-21mm and elevated enterococci levels over 700 MPN/100ml are associated with rainfall ranging from 12-35mm. Conclusion: A causal relationship between enterococci levels in recreational waters and rainfall events exists. Enterococci levels increase following rainfall events of 5mm and over in the majority of sampling sites along the Swan and Canning Rivers during five consecutive bathing seasons. Although environmental and faecal pol- lutions also contribute to recreational water quality, summer rainfall data has indicated that recreational water bodies experience periods of increased enterococci levels as rainfall volumes increase. Keywords: Enterococci level, microbial assessment category, NHMRC guidelines, rainfall, recreational water, water quality.