Harmful algal blooms (HABs) are events in which microscopic algae, cyanobacteria, or macroalgae grow or accumulate in marine or freshwater environments and cause harm. They can develop when conditions such as sunlight, temperature, nutrient availability, and water circulation favor certain organisms. Nutrient runoff and climate-related changes can also intensify some blooms. 

HABs may produce toxins, deplete dissolved oxygen from the water, block sunlight, or physically damage aquatic organisms, threatening human and animal health, ecosystems, drinking-water supplies, fisheries, recreation, and local economies. 

NASA has some of the world’s best Earth-observation platforms for detecting and analyzing harmful algal blooms for the benefit of environmental science and human safety.