Harmful algal blooms (HABs) are the rapid growth of algae or cyanobacteria that can cause harm to people, animals, or the local ecology. Harmful algae or cyanobacteria can look like foam, scum, paint, or mats on the surface of water and can be different colors. These blooms can produce toxins that make people and animals sick. Blooms occur in fresh water, such as lakes and rivers, and salt water, such as oceans or bays (CDC 2021).
Algae and cyanobacteria are simple organisms that live in the water. Algae and cyanobacteria can rapidly grow out of control, or “bloom,” when water is warm, slow-moving, and full of nutrients. Many types of algae do not produce toxins and not all visible algae is harmful. Explore the "how to identify" page or visit DEC's Harmful Algal Blooms Photo Gallery.
