Algal Bloom

An algal bloom is a rapid increase in phytoplankton or macroalgal biomass in a water body, usually driven by nutrient enrichment, warm stratified water, and high light. Diatoms, dinoflagellates, and cyanobacteria are common bloom formers, with cell counts rising from thousands to millions per liter over days. Most blooms are part of normal seasonal productivity, but excess nitrogen and phosphorus from agricultural and urban runoff push them past the assimilative capacity of the receiving water. As the bloom collapses, bacterial decay consumes dissolved oxygen and can drive hypoxia. Some blooms turn harmful through biotoxins or sheer biomass. Satellites track surface chlorophyll-a to map bloom extent.