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NC Department of Health and Human Services
NC Division of Public Health
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Occupational & Environmental Epidemiology

Cyanobacteria (Blue-green Algae)

Algae are very tiny, often microscopic, plants or plantlike organisms that live in water or damp areas. One type of freshwater algae increasingly seen in North Carolina is cyanobacteria (blue-green alage), which may actually look reddish-brown as well as bright green or blue-green. Many types of algae flourish in lakes and ponds with poor water flow, especially during the hot months of the year.

When conditions are right, blue-green algae can multiply and accumulate rapidly, causing a "bloom." The algae bloom may turn the water neon green, blue-green, or reddish-brown; may cause a bad smell and taste in the water; and may form a foam or scum on the water's surface. The algae may periodically use up oxygen in the water, killing fish. It can also affect other animals and people. The algae can cause skin irritation or respiratory irritation in people who get in the water or handle the algae. Some blooms of blue-green algae can produce chemicals that are toxic to animals and people who drink the untreated water. The presence or absence of a bad smell or taste is not a reliable indicator of the presence or absence of algal toxins in the water.

Although there are no documented reports of people getting sick from blue-green algae in North Carolina, people should follow these common-sense, practical precautions around blue-green algae blooms:

  • Don't wade or swim in water containing visible blooms, and avoid direct contact with dense mats of algae.
  • Don't drink untreated water or let children, livestock or pets get into or drink untreated water.
  • Make sure children are supervised at all times when they are near water. Drowning, not exposure to algae, remains the greatest hazard of water recreation.
  • If you do come into contact with the algae or water around a bloom, simply rinse off with fresh water as soon as possible.
  • Please see also our guidelines specifically for the protection of children and dogs.

Public drinking water supplies are carefully monitored at water treatment plants and by the N.C. Public Water Supply Section to ensure safe drinking water. Algae can be removed from drinking water by filtration, and unwanted odors and tastes caused by algae are removed with activated carbon and potassium permanganate during water treatment.

Facts and Figures

For Additional Information

  • CDC: Harmful algal blooms External link
  • Contact the Occupational and Environmental Epidemiology Branch of the Division of Public Health at (919) 707-5900.