When are algal blooms harmful?

At times, blue-green algae can reproduce very rapidly, creating a dense growth known as a bloom. Some species or strains of blue-green algae produce toxins, which can be released when they become stressed and/or die. It is still not fully understood why these compounds are produced - whether they are adaptations that benefit the organism, or whether they are merely by-products of some other important process. Some other types of algae can also produce harmful blooms; the famous marine “red tides,” produced by overgrowth of red algae, are an important example.

Blue-green algae are the culprits behind harmful algal blooms (HABs) in Kansas. They can have the ability to produce toxins, and even non-toxic blooms can cause skin irritation. Not all strains of a given species produce toxins, but most of the potentially harmful blue-green algae that have been seen in Kansas belong to one of three genus groups: Microcystis, Aphanizomenon, and Dolichospermum (formerly called Anabaena).

Due to the potential size of the blooms created by these groups and the possibility of the toxin production, a blue-green algae bloom is often known as a harmful algal bloom, or HAB. If the water is scummy, has a thick mat of growth, or is foamy, it can be an indication that there is a HAB present. Another indicator of a potential HAB is the color. The water could be colored pea-green, blue, or blue-green, and a cyanobacterial bloom can look like a vivid paint spill or floating grass clippings.

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1. What are algae?
2. What do the different terms mean?
3. When are algal blooms harmful?
4. What causes blue-green algae blooms?
5. For more information