Blue-Green Algae and Harmful Algal Blooms
Blue-green algae are not algae at all but are photosynthetic bacteria, also known as cyanobacteria. There are several species of blue-green algae, which thrive under their own unique conditions and produce a variety of toxins. Blue-green algae are naturally occurring and usually present in a water body, but they typically exist in numbers too small to cause problems. Blue-green algae growth is influenced by a variety of environmental conditions including temperature, flow, nutrient levels, light, weather, vertical mixing in the water column, and pH levels.
Given the right conditions, high concentrations of blue-green algae can occur and form a bloom. Blooms can vary in appearance, sometimes looking like mats, foam, or surface scum. Blooms can range in color from blue and bright green to brown and red. Some blooms produce a foul odor. Not all blooms are toxic, but when toxic harmful algal blooms do occur they present a health risk to humans, pets, and livestock. Exposure may occur from ingestion, skin contact, or inhalation. Exposure can result in a range of health effects from skin irritation and stomach upset to neurotoxic effects and at very high levels, death. Symptoms in humans are rare; anyone with symptoms should seek medical attention.
If you observe a blue-green algae bloom, contact your DEQ regional office.
Health advisories are typically issued by the public health districts, who work closely with DEQ staff.
Take the following precautions when an advisory is in effect:
- Avoid exposure to water experiencing a harmful algal bloom. Take extra precautions to ensure children, pets, and livestock are not exposed to the water.
- Do not consume water with a blue-green algae bloom. Neither boiling nor disinfecting removes blue-green algae toxins from water.
- If fish are known to have been exposed to a blue-green algae bloom, only consume the fillet portion (remove the fat, organs, and skin). Wash hands after handling. The risk associated with consuming fish caught in waters with a blue-green algae bloom is unknown. Toxins produced by blue-green algae can accumulate in the organs of fish.