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Swimming water quality and blue-green algae

The hygienic quality of swimming water in the beaches of Helsinki is assessed by studying the prevalence of intestinal enterococci and Escherichia coli. Large public beaches in Helsinki are sampled four times during the swimming season, while small public beaches are sampled four times.

The amount of blue-green algae is assessed organoleptically in connection with the sampling.

Swimming water quality classification

The water quality of the large public beaches of Helsinki was categorised into four categories (excellent, good, adequate and poor. The classification is based on water quality samples taken during the swimming seasons of 2016–2019. The classification is affected by the amounts of intestinal enterococci and Escherichia coli found in the samples. The classifications are updated annually.

Excellent: Aurinkolahti, Kallahdenniemi, Laajasalo, Munkkiniemi, Mustikkamaa
Good: Hietaranta, Lauttasaari, Rastila, Tuorinniemi
Adequate: Iso Kallahti, Marjaniemi, Pikkukoski
Poor: -

Blue-green algae

The amount of blue-green algae usually starts to increase in July and peaks at the turn of July and August. The toxicity of blue-green algae depends on the species of algae and the environmental conditions. Even in a single algal bloom, some of the algae mass may be toxic, while the rest is harmless, so blue-green algae should always be treated as if it is toxic.

Outdoor Exercise Map

In the Outdoor Exercise Map service you can find information on the beaches in the metropolitan area – the algae situation and the water temperature. (in Finnish).

Identifying blue-green algae

Blue-green algae are visible in the water as small amounts of greenish or yellowish sticks or nuggets. Large amounts of blue-green algae may gather on the water’s surface into algal blooms. Algal mass that ends up on a shore may resemble thick paint or pea soup. Blue-green algae typically have a mouldy, soil-like smell.


The amount of blue-green algae is assessed organoleptically. Swimming in water in which blue-green algae has been observed should be avoided. Small children should not be let into the water during blue-green algal blooms, as they might ingest water that contains blue-green algae. Water that contains blue-green algae should also not be used for washing or as sauna water.

If you wish to swim despite the occurrence of blue-green algae, you should wash up with clean water immediately after swimming.


Blue-green algae may produce toxic or irritating substances in the water. Blue-green algae have been known to cause rashes, irritation of the eyes and fevers, among other symptoms.

04.05.2020 15:11