Concerns about pathogens in drinking, recreation, irrigation, aquaculture, and other types of waters have been increasing over the past decades. Microbial water quality is currently evaluated using concentrations of faecal indicator organisms (FIOs). FIOs are not pathogenic, but their presence in the aquatic environment does indicate contamination with material of faecal origin, with higher concentrations of FIOs suggesting increased risk of connectivity between receiving waters and FIO sources which may also potentially harbor and release pathogens. Monitoring and modelling of microbial water quality in complex catchments is therefore of paramount importance for both environmental and human health protection. Hydrological activity can impact on FIO mobilization, transport and delivery through catchment systems and affect their export from both point and nonpoint sources. Soil and aquatic microbial and algal communities alter the survival patterns of FIOs, which are then moderated further by abiotic environmental controls. This session welcomes experimental and modeling research that aims to improve our understanding of FIO dynamics in catchment systems in order to inform stakeholders of microbial water quality and to evaluate potential health risks associated with site-specific conditions. Effects of mitigation and management practices on FIO fate and transfer at multiple scales will also be of interest.