Algicide, also known as algaecide, is a chemical substance formulated to control and prevent the growth of algae in water systems such as swimming pools, fountains, cooling towers, lakes, and industrial water treatment facilities. It works by disrupting the cellular processes of algae, thereby inhibiting photosynthesis and reproduction. Algicides are available in various formulations including quaternary ammonium compounds (quats), polyquats, copper-based solutions, and non-metallic blends. It is typically used as part of regular water treatment programs to maintain clarity, hygiene, and biofilm control.