page_title: Harmful algal bloom
section_title: Types
hierarchical_section_title: Harmful algal bloom / Types
caption_attribution_description: English: Blue green algae bloom on the shore of Catawaba Island, Ohio in Lake Erie. Summer 2009.
context_page_description: A harmful algal bloom contains organisms that can severely lower oxygen levels in natural waters, killing marine life. Some HABs are associated with algae-produced toxins. Blooms can last from a few days to many months. After the bloom dies, the microbes which decompose the dead algae use up even more of the oxygen, which can create fish die-offs. When these zones of depleted oxygen cover a large area for an extended period of time, they are referred to as dead zones, where neither fish nor plants are able to survive.
  HABs are induced by an overabundance of nutrients in the water. The two most common nutrients are fixed nitrogen and phosphate. These nutrients are emitted by agriculture, other industries, excessive fertilizer use in urban/suburban areas and associated urban runoff. Higher water temperature and low circulation are contributing factors. HABs can cause significant harm to animals, the environment and economies. They have been increasing in size and frequency worldwide, a fact that many experts attribute to global climate change. The U.S. National Oceanic and Atmospheric Administration predicts more harmful blooms in the Pacific Ocean.
context_section_description: There are three main types of algae which can form into harmful algal blooms: cyanobacteria, dinoflagellates and diatoms. All three are made up of microscopic floating organisms which, like plants, can create their own food from sunlight by means of photosynthesis. That ability makes them an essential part of the food web for small fish and other organisms.
caption: Cyanobacteria (blue-green algae) bloom on Lake Erie in 2009
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