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Harmful Algal Blooms

Tiny Plants with a Toxic Punch

Harmful algal blooms, or HABs, occur when colonies of algae—simple plants that live in the sea and freshwater—grow out of control while producing toxic or harmful effects on people, fish, shellfish, marine mammals, and birds. The human illnesses caused by HABs, though rare, can be debilitating or even fatal. HABs have been reported in every U.S. coastal state, and their occurrence may be on the rise. HABs are a national concern because they affect not only the health of people and marine ecosystems, but also the 'health' of local and regional economies.

scientists sampling for HAB cysts
HAB Research

Harmful algal blooms occur naturally, but human activities that disturb ecosystems seem to play a role in the increased occurrence of some blooms. NOAA is authorized by the Harmful Algal Bloom and Hypoxia Research and Control Act to help communities counter this increasing threat with research.

microscopic view of HAB
Phytoplankton Monitoring Network

The Phytoplankton Monitoring Network is made up of volunteers who monitor for marine phytoplankton and HABs in cooperation with professional scientists. This effort builds a more informed public while expanding the reach and resolution of HAB monitoring.