This technical brief provides general information on the management of cyanobacteria in drinking-water supplies to help regulators and water suppliers safeguard public health. It  describes measures to prevent the formation of cyanobacterial blooms and options to manage such blooms and their toxins when they occur. This updated technical brief has been revised based on the second edition of Toxic cyanobacteria in water – a guide to their public health consequences, monitoring and management.