Harmful algal blooms (HABs) caused by Microcystis species are a growing threat to water quality, ecosystem health, and recreational resources. Conventional algicide treatments often require repeated applications and may lose effectiveness due to rapid dilution and degradation in aquatic environments. This project aims to develop a sustainable biochar-based controlled-release algicide system for long-term HAB mitigation. Building on our previous work utilizing functionalized biochar from forest residue biomass (FRB) for nutrient capture, we will evaluate Fe-functionalized biochar as a carrier for three representative algicides: copper sulfate, a copper–ethanolamine complex, and a peroxide-releasing formulation. The project will investigate algicide loading capacity, release kinetics, and controlled-release behavior under simulated aquatic conditions, followed by laboratory studies evaluating inhibition of Microcystis aeruginosa growth and bloom formation. The resulting data will establish design principles for biochar-based slow-release algicide systems that provide sustained bloom suppression while reducing chemical usage and minimizing impacts on non-target organisms. This work will create a value-added application for FRB and lay the foundation for future field deployment of sustainable HAB management technologies.