Water Sanitation Health

Guidelines for safe recreational water environments
Volume 1 : Coastal and fresh waters

Executive summary


Algae and cyanobacteria in coastal and estuarine waters

Several human diseases have been reported in association with many toxic species of dinoflagellates, diatoms, nanoflagellates and cyanobacteria (blue-green algae) that occur in the marine environment. The toxicity of these algae to humans is due to the presence of algal toxins. Marine algal toxins become a problem primarily because they concentrate in shellfish and fish that are subsequently eaten by humans, causing shellfish poisoning.

Marine cyanobacterial dermatitis (“swimmers’ itch” or “seaweed dermatitis”) is a severe contact dermatitis that may occur after swimming in seas containing blooms of certain species of marine cyanobacteria. The symptoms are itching and burning within a few minutes to a few hours after swimming in the sea where the cyanobacteria are suspended. Some toxic components, such as aplysiatoxin, debromoaplysiatoxin and lyngbyatoxin A, have been isolated from marine cyanobacteria. These toxins are highly inflammatory and are potent skin tumour promoting compounds.

Nodularia spumigena was the first cyanobacterium recognized to cause animal death. The toxin produced by N. spumigena, called nodularin, acts as a hepatotoxin, in that it induces massive haemorrhages in the liver of mammals and causes disruption of the liver structure. To date, there have been no reports of human poisoning by N. spumigena, but humans may be as susceptible to the toxins as other mammals. Therefore, it is possible that small children may accidentally ingest toxic material in an amount that may have serious consequences.

Inhalation of a sea spray aerosol containing fragments of marine dinoflagellate cells and/or toxins (brevetoxins) released into the surf by lysed algae can be harmful to humans. The signs and symptoms are severe irritation of conjunctivae and mucous membranes (particularly of the nose) followed by persistent coughing and sneezing and tingling of the lips.

Available data indicate that the risk for human health associated with the occurrence of marine toxic algae or cyanobacteria during recreational activities is limited to a few species and geographical areas. As a result, it is inappropriate to recommend specific guideline values.

Within areas subject to the occurrence of marine toxic algae or cyanobacteria, it is important to carry out adequate monitoring activities and surveillance programmes. In affected areas, it is appropriate to provide health information to general practitioners and the general public, in particular recreational water users. Precautionary measures include avoiding areas with visible algal concentrations and/or algal scums in the sea as well as on the shore, avoiding sitting downwind of any algal material drying on the shore and showering to remove any algal material.

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