Algal bloom

An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems, and is recognized by the discoloration in the water from their pigments. Cyanobacteria were mistaken for algae in the past, so cyanobacterial blooms are sometimes also called algal blooms. Blooms which can injure animals or the ecology are called 'harmful algal blooms' (HAB), and can lead to fish die-offs, cities cutting off water to residents, or states having to close fisheries. A bloom can block the sunlight from reaching other organisms, deplete oxygen levels in the water, and some algae even secrete toxins into the water.