Algae are small photosynthetic organisms found in almost every environment on Earth. Under the right conditions, such as high nutrients and sunlight, algae can grow rapidly and "bloom." Algal blooms often accumulate on the surface of water bodies, giving the water a green, brown, or red appearance.
A Harmful Algal Bloom (HAB) is a bloom of certain types of algal species that produce toxins as it blooms or dies. These toxins may harm wildlife and humans when ingested or inhaled. In the Great Lakes, the algal species that are commonly associated with HABs are the cyanobacteria or blue-green algae known as Microcystis.