Suomen ympäristökeskus

Blue-green algae situation has remained stable both in lakes and at sea


Blue-green algae observations in lakes and coastal areas have increased slightly since last week. However, the situation is normal for the season and, in lakes, even better than usual. In sea areas, blue-green algae close to the surface have been observed mainly in the eastern parts of the Gulf of Finland. Elsewhere in the open sea, blue-green algae are mixed with water.

Satellite images showed blue-green algae west of Upinniemi on Tuesday 15 August 2023.
Satellite images showed blue-green algae west of Upinniemi on Tuesday 15 August 2023.
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Map of the national blue-green algae monitoring observations of the review week. A link to the map can be found below.

Link to the map

Map of the national blue-green algae monitoring observations on week 33 

More in Finnish

Sinilevätilanne pysynyt tasaisena niin järvillä kuin merellä

Syke observes the cyanobacteria occurrence as part of the monitoring of the state of the environment in Finland 

The national cyanobacterial monitoring is carried out as part of the monitoring of the state of the environment in cooperation with the Centres for Economic Development, Transport and the Environment, municipal environmental and health authorities, and the Finnish Environment Institute (Syke). Finnish Rotary Clubs are also actively involved in nationwide cyanobacterial monitoring. 

The cyanobacterial monitoring is based on the monitoring of cyanobacterial deposits in surface water. The intention is to provide an overview of the cyanobacterial situation in different water bodies. The monitoring includes about 400 permanent observation sites across the country on inland and coastal waters and in the archipelago. 

Information on the cyanobacterial situation in the open sea areas is mainly obtained from satellite images, but also from the Finnish Border Guard, the marine research vessel Aranda, the optical device located at the Utö Atmospheric and Marine Research Station, as well as cruise and merchant ships (MS Finnmaid and MS Silja Serenade) equipped with Alg@line measuring equipment. The drift forecasts for cyanobacterial rafts in open sea areas are prepared in cooperation with the Finnish Meteorological Institute's Maritime Services. 

Syke reports on the national cyanobacterial situation on a weekly basis every Thursday from the beginning of June until the end of August. The weekly algal reporting was launched in 1998. 

Several compounds produced by cyanobacteria can cause health hazards 

According to the Finnish Institute for Health and Welfare (THL), cyanobacterial occurrences can cause health hazards. Cyanobacteria produce a number of different compounds that can cause symptoms. Some cyanobacteria can produce liver or nerve toxins, but most of the symptoms experienced by swimmers may also be due to other compounds. 

Small children and pets should particularly be kept out of water rich with cyanobacteria. Water with cyanobacteria should not be used in a sauna or as washing or irrigation water. 

If you suspect a poisoning, seek medical advice, or take the pet to a veterinarian. If necessary, the Poison Information Centre will provide additional instructions. 

The municipal health authorities monitor the cyanobacterial situation on beaches. 

More information about blue-green algae and health:

Report your cyanobacterial observations to the Järvi-meriwiki (Lake and sea wiki) 

In Järvi-meriwiki,  maintained by the Finnish Environment Institute, you can establish your own observation site and share cyanobacterial observations or make individual observations when moving around waterways. You can also report observations via the smartphone-friendly Havaintolähetti website. 

The reported observations are shown on the national cyanobacterial observation map, and they support the national algal situation assessment. Observations about the absence of cyanobacteria are also important. 

Järvi-meriwiki is an online service produced in collaboration with authorities and citizens. The service provides basic information on all lakes larger than one hectare as well as different areas of the Baltic Sea. Users can share, for example, photos and other observations on the service. 

Municipalities and cities monitor the cyanobacterial situation on the beaches, so it is advisable to report rich cyanobacterial occurrences on beaches to the health authorities of the municipality in question. 

This is how you identify cyanobacteria 

A small amount of cyanobacteria in the water appears as green or yellowish particles. Narrow stripes of algae can drift to a beach. In calm weather, a substantial amount of cyanobacteria forms greenish or yellowish algal rafts and piles up in coastal water. In spring, yellowish pollen from coniferous trees may also be present in the water. Unlike cyanobacteria, pollen is found not only on the surface water but also, for example, on piers or yard furniture. 

Cyanobacteria dissolve into tiny particles in the water if you touch the algal mass with a stick. If the algae become attached to the stick, they are something other than cyanobacteria. In a water vessel, cyanobacteria rise to the surface as tiny greenish particles within about an hour. 

Cyanobacterial observations also in the and services 

The cyanobacterial maps presented on the websites  and   combine the observations reported to the Järvi-meriwiki and from the beaches of the City of Helsinki, as well as the observations based on satellite interpretations made by Syke during the last three days. 



Inquiries about blue-green algae situationTelephone 1 pm to 3 pm

Lakes: Tel +358 50 5734 347 or +358 295 251 326

State of the Baltic Sea: Tel +358 50 5693 297 or +358 295 251 314

Satellite observations: Tel 358 50 4707 576 or +358 295 251 329, e-mail:


Satellite images showed blue-green algae west of Upinniemi on Tuesday 15 August 2023.
Satellite images showed blue-green algae west of Upinniemi on Tuesday 15 August 2023.


It is time to move beyond solving environmental problems one by one, to systemic sustainability transformations. The Finnish Environment Institute (Syke) contributes to building a sustainable society through research, information and services. The Finnish Environment Institute is a research institute with 700 experts and researchers located in Helsinki, Oulu, Jyväskylä and Joensuu.

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