Algae in the shore water of the sandy beach, no alga deeper.
Blue-green algae at Ukonlinna beach in Imatra

Identify blue-green algae and assess the risks - instructions for blue-green algae

28.6.2022 12:54
The observation of blue-green algae in water areas is based on the observations and reports of individuals, as well as observations made in connection with sampling and monitoring by the authorities.

The national blue-green algae situation can be monitored by the state environmental administration In the Järviwiki service. Both assessments made by the authorities and observations made by citizens are updated there. In the service, you can also familiarize yourself with the blue-green algae observations made by others.

You can easily record your algae observations To the Havintovähetti service, through which the findings are published in Järviwiki's algae monitoring. You should also always report blue-green algae sightings on public beaches to the health protection authority and the beach administrator. The contact information of the health protection authority and the beach administrator can be found on the bulletin boards of swimming beaches and on the websites of the municipalities.

The municipal health protection authority that supervises public swimming beaches does not visit the beaches every day to assess the presence of blue-green algae and does not provide information on the blue-green algae situation on a daily basis. It is also worth noting that only observations reported or made there are displayed on different monitoring websites. The blue-green algae situation may change quickly.

Before swimming, you should always visually assess the condition of the swimming water.

What is blue-green algae?

Blue-green algae are a natural part of aquatic life, but when they become abundant they can cause problems, as some species are poisonous. About half of the mass occurrences of blue-green algae have been found to be toxic.

Blue-green algae are microscopically small, single-celled algae that form colonies of various shapes. Depending on the species, the community can appear in the water as small flakes or sharp sticks. When it becomes abundant, it forms bands and algal rafts and colors the water, sometimes making it look like latex paint. Blue-green algae mass usually smells earthy and musty.

The toxicity of the species varies and can only be determined by laboratory tests. 

The visible mass of blue-green algae is called a bloom, even though it does not actually form any flowers. It is difficult to predict and control the occurrence and duration of blooms, i.e. blue-green algae blooms. Winds and currents can move the blue-green algae mass, so the amount of blue-green algae in the water can change quickly even during the same day. Blue-green algae deposits start to appear as the waters warm, and they may continue well into autumn. The abundance and extent of occurrences varies annually depending on weather conditions and nutrients.

How can you identify blue-green algae?

Blue-green algae can be identified with a drinking glass or stick test, performed by the Finnish Health and Welfare Institute THL has also illustrated with a picture.

During the drinking glass test, the water stands in the glass for about an hour, during which the blue-green algae rises to the surface. However, blue-green algae does not always rise to the surface, but is visible in the water as green bits. The water should therefore be examined carefully before possible use. The small green particles on the surface are blue-green algae.

In the stick test, you try to lift the algae mass into the air with a stick. If the algal mass breaks down into small green particles in the water, the alga is blue-green algae.

What are the side effects of blue-green algae and when should you seek treatment?

Some blue-green algae can produce liver or nerve toxins. In addition to toxins, blue-green algae can produce compounds that irritate the skin, among other things. Based on the appearance of the blue-green algae deposit, it is not possible to judge whether it is a toxin-producing blue-green algae species or not.

People's sensitivity to symptoms caused by blue-green algae varies. Symptoms usually appear within a few hours of exposure to blue-green algae.

Blue-green algae can cause skin symptoms, stomach symptoms (e.g. nausea, stomach pain, diarrhea, vomiting), or flu-like symptoms, such as runny nose, headache, eye irritation and fever.

If you have symptoms or suspect that you swam in blue-green water, wash thoroughly with plenty of clean water and soap. Usually the symptoms go away without treatment, and if necessary, you can take fever and pain medicine.

If the symptom is also abundant vomiting and diarrhea, there is a risk of dehydration. In that case, you should seek treatment by calling Eksoten's emergency number 116 117. Similarly, skin swelling symptoms that require treatment combined with abundant redness or difficult respiratory symptoms are reasons to seek emergency care. You can also ask for advice from the HUS Poison Information Center on 0800 147 111.

How to avoid the side effects of blue-green algae?

It is impossible to estimate the duration of the presence of blue-green algae. If your water has, or you know has recently had, blue-green algae, remember these things:

  • Do not swim in blue-green algae water
  • Do not allow children or pets to play or swim in the beach water
  • The water must not be used as drinking water for humans or animals, even when boiled
  • The water must not be used as soaking water
  • The water is not recommended as washing water
  • The water is not recommended as dishwater
  • Water is not recommended for watering edible plants

For more information: 

Environmental action of the Imatra region, health controlatimatra.fi (health control[at]imatra[dot]fi)
environmental engineer Marcella Suomalainen, tel. 020 617 4324, marcella. Finnishatimatra.fi (marcella[dot]suomalainen[at]imatra[dot]fi) 
environmental engineer Sirpa Heinänen, tel. 020 617 4391, sirpa.heinanenatimatra.fi (sirpa[dot]heinanen[at]imatra[dot]fi)