From Bloom Suppression to Durable Risk Reduction: An Intervention Audit for Recurrent Freshwater CyanoHABs

Recurrent freshwater cyanobacterial harmful algal blooms (CyanoHABs) are often managed as isolated episodes. Rapid clearing can leave nutrient stores, sediment recycling, benthic recruitment, and food web instability largely unchanged. This critical narrative review summarizes intervention roles, failure modes, and monitoring needs using a structured inventory of 53 selected core sources, with contextual reviews and guidance. Searches covered PubMed, selected publisher interfaces, and citation tracing through 27 September 2026; the inventory is not an exhaustive or systematic evidence map. Of 30 empirical sources, only seven extend beyond six weeks, including one 56-day mesocosm, so evidence for sustained recurrence reduction is limited. We distinguish Tier 1 (prevention and ecological stabilization), Tier 2 (targeted response and localized exposure reduction), and Tier 3 (restricted emergency containment). The proposed Intervention Decision Audit adapts established adaptive management and impact assessment principles into a practical checklist linking the recurrence mechanism, study scale and follow-up, intervention choice, safeguards, responsible authority, exit conditions, and outcome evaluation. Its contribution is this explicit linkage for recurrent CyanoHAB decisions, rather than new principles of adaptive management. Success should be assessed through bloom recurrence and duration, toxin and exposure risk, ecological condition, and dependence on repeated emergency treatment. The checklist has not yet been prospectively validated in management practice.