Cyanobacteria Harmful Algal Blooms
Cyanobacteria are photosynthetic bacteria that occur naturally in Idaho’s lakes and rivers. Many of us learned about “blue-green algae” in school, but these algae are actually bacteria that photosynthesize like algae and plants. The photosynthetic structures within the bacterial cell contain the blue-green pigments that gave cyanobacteria their former name of “blue-green algae.” Cyanobacteria are present in a water body but typically exist in numbers too small to cause problems (sight, smell, and cyanotoxins). However, a variety of environmental conditions influence cyanobacteria population growth. The right summer time conditions can allow cyanobacteria populations to “bloom” to high enough numbers that a variety of toxins, known as cyanotoxins, are produced. These ideal conditions include warm temperatures, low or slow water flow, high nutrient levels, strong light, and calm weather.
Cyanobacteria harmful algal blooms (HABs) in Idaho can vary in appearance, often looking like pollen, grass clippings, spilled paint, mats, foam, or a dense surface scum. Blooms can range in color from blue and bright green to brown, red, and even white. Some blooms may produce a foul odor.
Cyanotoxins can present a real threat to people and animals. Cyanotoxins are thought to primarily be metabolites and used for taking in nutrients. Toxin exposure primarily occurs from ingesting the cyanobacteria and the water they live in but may also occur with skin contact. Ingesting cyanotoxins, which can remain after a visible HAB subsides, 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 HAB, contact your DEQ regional office. If in doubt, stay out!
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 HAB. Take extra precautions to ensure children, pets, and livestock are not exposed to the water.
- Do not consume water with a HAB. Neither boiling nor disinfecting water removes cyanotoxins from water.
- Consume only the fillet portion of fish exposed to a HAB. Cyanotoxins can accumulate in fish. Removing the fat, organs, and skin minimizes the exposure. Wash hands after handling. The risk associated with consuming fish caught in waters with a HAB is unknown and under research.