Missing the middle: Deep cyanobacteria layers pose a “known unknown” risk to water security

Deep cyanobacteria layers are an emerging concern in harmful algal bloom research, posing a “known unknown” risk to human health. A known unknown risk is one of which society is aware but cannot accurately assess the potential impacts due to insufficient research. Deep cyanobacteria layers develop below the surface. At this depth, the presence of cyanobacteria is not casually recognized and therefore seldom evokes public health concerns or advisories. However, the potential risk of deep cyanobacteria layers to public health places heightened importance on learning more about depth-differentiation among phytoplankton. We identify four scientific gaps about deep cyanobacteria layers. Advancing our understanding by filling these scientific gaps is crucial to reducing the risks associated with deep cyanobacteria layers to human health and safeguarding water security.