Managing cyanobacterial blooms in recreational waters: decision support tools for public health responses

Freshwater blooms of cyanobacteria present a challenge to those tasked with managing beaches during bathing season, both to ensure the protection of public health, and to avoid lengthy beach closures. The combined effects of climate change and environmental pollution could cause blooms to become more frequent, intense, and persistent in the future in some locations, necessitating regularly review and update of response protocols. Decision support tools are used to help manage bloom events and inform responses. These can advise on the triggers for inspection, testing, posting of advisories, closing of beaches, and when to rescind advisories and reopen beaches. The aim of this paper was to present an overview of approaches and decision support tools used to inform public health responses to cyanobacterial blooms. During bathing season in Canada, most bloom monitoring is reactive, with a limited coverage of proactive monitoring, except at priority beaches. Responses to blooms vary widely, but many are informed by decision protocols or flow charts using visual inspection and single-level indicators, or alert level frameworks using multiple indicators and alert levels. The only health-based indicators used in any system are cyanotoxins, but capacity for frequent testing is often limited. Approaches to rescinding advisories also vary in the types of indicators and length of time used to determine when it is safe to resume recreational activities. This can vary from days to weeks, with some jurisdictions taking more precautionary approaches. Responsible authorities must balance public health protection with available resources for testing and monitoring with public acceptance of extended beach closures. With the prospect of more frequent and pervasive blooms in the future, there will be a need to allocate scare resources efficiently, which may require regular review and update of response protocols. Adapting approaches may require using a range of more accessible indicators alongside local knowledge, site history, and new tools to inform site-specific responses.