Region-Specific Associations between Environmental Factors and Escherichia coli in Freshwater Beaches in Toronto and Niagara Region, Canada

Abstract

Poor freshwater beach quality, measured by Escherichia coli (E. coli) levels, poses a risk of recreational water illness. This study linked environmental data to E. coli geometric means collected at 18 beaches in Toronto (2008–2019) and the Niagara Region (2011–2019) to examine the environmental predictors of E. coli. We developed region-specific models using mixed effects models to examine E. coli as a continuous variable and recommended thresholds of E. coli concentration (100 CFU/100 mL and 200 CFU/100 mL). Substantial clustering of E. coli values at the beach level was observed in Toronto, while minimal clustering was seen in Niagara, suggesting an important beach-specific effect in Toronto beaches. Air temperature and turbidity (measured directly or visually observed) were positively associated with E. coli in all models in both regions. In Toronto, waterfowl counts, rainfall, stream discharge and water temperature were positively associated with E. coli levels, while solar irradiance and water level were negatively associated. In Niagara, wave height and water level had a positive association with E. coli, while rainfall was negatively associated. The differences in regional models suggest the importance of a region-specific approach to addressing beach water quality. The results can guide beach monitoring and management practices, including predictive modelling.

Environmental predictors of Escherichia coli concentration at marine beaches in Vancouver, Canada: a Bayesian mixed-effects modelling analysis

“…Our mixed-methods analysis showed a positive average effect of the log geometric mean of E. coli in the previous sample day on geometric mean E. coli concentration, consistent with previous studies elsewhere [ 38 – 40 ]. Even though beach water sampling was not conducted daily in Vancouver, the positive effect of the previous sample day log E. coli values on the E. coli concentration could indicate the persistence of contamination levels in marine water bodies over several days, conditional on other environmental factors.…”

“…Still, it is not always the case that such relationships are that different by beach, though they were in this study. For example, in a similar study in Toronto and Niagara, the Niagara beaches were very similar probably due to proximity and most had really excellent water quality, so it might be related to both of those factors and common/different pollution sources [ 40 ].…”

Recreational water exposures and illness outcomes at a freshwater beach in Toronto, Canada: A prospective cohort pilot study

“…It received the Blue Flag designation in 2022 as well as prior years, an international certification program that assesses water quality and other environmental and safety criteria [28]. However, elevated E. coli levels occasionally occur throughout the summer season leading to swimming advisories [28,29], suggesting one or more recurring sources of fecal contamination.…”

Environmental factors associated with Escherichia coli concentration at freshwater beaches on Lake Winnipeg, Manitoba, Canada

“…Multiple pollution sources and various environmental factors play a role in the fecal contamination of recreational waters [12]. Numerous studies have found that fecal contamination of fresh lake water is associated with recent rainfall [13][14][15]. The growth and survival of FIB in freshwater can also be determined by air and water temperature [14,16].…”

“…Numerous studies have found that fecal contamination of fresh lake water is associated with recent rainfall [13][14][15]. The growth and survival of FIB in freshwater can also be determined by air and water temperature [14,16]. The FIB concentration in fresh lake water also tends to decrease with increased ultraviolet (UV) solar radiation [14].…”