Is Black Algae in a Swimming Pool Harmful?

Swimmers will not be harmed by the presence of black algae in a swimming pool. The black or bluish-green spots will be a deterrent to swimmers; however, similar to garden weeds, black algae is a nuisance but will not, by itself, cause illness.

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Prevent black algae with regular maintenance and balanced pool chemicals.

Black Algae Does Not Cause Illness

Black Algae Harbors Harmful Organisms

Black algae may harbor organisms, such as E. coli, which can make swimmers quite ill. In addition, swimmers will need to remain out of the water while the pool is being treated; heavy doses of chemicals such as pool shock and algaecide must circulate for several hours prior to the water chemistry reaching safe levels.

Bottom Line

Swimmers should think twice before diving into a pool affected by black algae. Algae can attract insects and harbor harmful bacteria which can make swimmers ill. Home owners should take preventative measures, such as regular brushing of pool sides and maintaining balanced chemical, to avoid black algae, if possible.


Caryn Anderson

Caryn Anderson combines extensive behind-the-scenes writing experience with her passion for all things food, fashion, garden and travel. Bitten by the travel bug at the age of 15 after a trip to Europe, Anderson fostered her love of style and fashion while living in New York City and earning her degree at New York University.