Cyanobacterial harmful algal blooms (cHABs) pose a significant environmental and public health threat that affects diverse water bodies, ranging from oceans, lakes, and reservoirs to aquaculture ponds and irrigation canals. A common approach to their early-stage management in many settings is the use of algaecides. However, their efficacy is often short-lived, requiring frequent reapplication. To extend treatment longevity, sustained-release algaecide formulations—such as coated granules or gel-based dispersions—have been developed. These approaches, however, have drawbacks, including much higher costs and susceptibility to displacement by wind, currents, or sedimentation. To address these challenges, here we explore the design and application of reusable buoys that (1) remain immobilized at targeted treatment sites, and (2) sustain the controlled release of conventional liquid algaecides for over a month. The controlled release is achieved by incorporating hydrogel-based diffusion barriers into the otherwise impermeable, algaecide-filled buoys. Close alignment between experimental measurements and model predictions demonstrates that release rates can be predictably tailored by adjusting buoy and gel barrier dimensions, as well as the initial algaecide concentration. Furthermore, micro- and mesocosm studies (performed using a commercial H2O2-based algaecide) show that these buoys provide multiweek algicidal effects, as measured by fluorometric chlorophyll-a, cyanobacteria, and green algae levels, along with DNA analysis. When deployed in limnocorrals after an initial algaecide treatment they significantly extend algicidal effectiveness compared to a single treatment alone. Collectively, these findings suggest that, if successfully scaled, this buoy-based sustained release technology could offer a longer-lasting, more targeted, and potentially cost-saving approach to cHAB mitigation, and its use in delivering other water treatment chemicals will also be briefly discussed.
