The inter-tidal zone is the pathway of input of enterococci to a subtropical recreational marine beach.

Efforts were made to evaluate the source of enterococci levels at a recreational beach. Four monitoring efforts were implemented which included tidal studies, hourly sampling, runoff sampling, and spatially intensive sediment sampling. Spatially intensive sediment sampling indicated that enterococci concentrations consistently decreased away from the inter-tidal zone, both seaward and landward. During dry conditions, the highest concentrations in the water were observed during high tide (71±48 CFU/100 mL) and lower concentrations were observed during low tide (4±3 CFU/100 mL). Runoff was characterised by very high levels (11,700 CFU/100 mL). Results from these monitoring efforts collectively showed that the source of enterococci to the study beach is geographically located within the inter-tidal zone. Wash-in from the inter-tidal zone through tidal action and runoff plays a major role in controlling enterococci levels within the water column. Such results are significant in identifying the source and transport mechanisms of enterococci, which can subsequently be used as part of a modelling effort aimed at predicting enterococci levels at recreational beaches.