An
algal bloom is a rapid increase or accumulation in the population of
algae (typically microscopic) in a water system.
Cyanobacteria blooms are often called blue-green algae. Algal blooms may occur in
freshwater as well as
marine environments. Typically, only one or a small number of
phytoplankton species are involved, and some blooms may be recognized by discoloration of the water resulting from the high density of pigmented cells.