Cyanobacterial observations have increased in both lakes and sea areas; the situation is typical for the late summer

Press release 2021-07-29 at 14:07
Many lakes have seen abundant or very abundant cyanobacteria in the past week. Sentinel-2 satellite image from southern Pirkanmaa on Monday, 26 July. Observations picked from Järvi-meriwiki between 26 and 27 July. © SYKE material, contains modified Copernicus Sentinel-2 data (2021)

Larger amounts of cyanobacteria have been observed in inland waters than in the previous week. The observations are concentrated in eutrophic lakes and bays in the southern parts of Finland. Cyanobacterial blooms have become more abundant along the coast and in the Archipelago Sea. In the open sea, significant cyanobacterial rafts have only been observed in the Bothnian Sea and in the western parts of the Gulf of Finland. In late summer, the pigment released from cyanobacterial blooms may discolour water and beaches turquoise blue.

Taken on Sunday 25 July, the Sentinel-3 satellite image illustrates the cyanobacterial situation in the areas surrounding Finland. The cyanobacterial raft in the open seas of the Bothnian Sea has remained visible in satellite images. On the coasts, the occurrence of blooms varies by region. In the Gulf of Finland, significant surface rafts have only been observed in the western parts. The close-ups off Porvoo and Hanko are Sentinel-2 satellite images from 26 July. © SYKE material, contains modified Copernicus Sentinel-2 and Sentinel-3 data (2021)

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SYKE observes the cyanobacteria occurrence as part of the monitoring of the state of the environment

The national cyanobacterial monitoring is based on the monitoring of cyanobacterial deposits in surface water, and the intention is to provide an overview of the cyanobacterial situation in different water bodies. Observations are 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. Finnish Rotary Clubs are also actively involved in nationwide cyanobacterial monitoring.

This summer, cyanobacterial 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 seas 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.

The Finnish Environment Institute usually 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 on the national cyanobacterial monitoring was launched in 1998.

Several compounds produced by cyanobacteria can cause health hazards

According to the guidelines of the National Institute for Health and Welfare (THL), water rich in cyanobacteria should always be treated in such a way that it may be harmful to health. 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.

Especially small children and pets should be kept out of water rich with cyanobacteria. Water with cyanobacteria should not be used in the sauna or as washing or irrigation water. If poisoning is suspected, seek medical advice or take your pet to a veterinarian. If necessary, the Poison Information Centre will provide additional instructions.

The municipal health authorities monitor the cyanobacterial situation on the beaches.

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

In the Järvi-meriwiki maintained by the Finnish Environment Institute, everyone has the opportunity to establish their own observation site and share cyanobacterial observations from lakes and coastal areas. Individual observations can also be sent, for example, from beachs or during boat trips. The observations can be submitted via the Havaintolähetti website and they displayed on the national cyanobacterial situation map supporting the national assessments of the cyanobacterial situation. Observations about the absence of cyanobacteria are also important.

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

Cyanobacterial observations also in the Itä and services

Last summer, for the first time, websites on the cyanobacterial observations on the Itä service and the service were also launched. The cyanobacterial map presented on this algal bloom observations page combines 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 of the Finnish Environment Institute during the last three days.

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. Unlike cyanobacteria, pollen is found not only on the surface water but also, for example, on piers or yard furniture.

If the algae dissolve into tiny particles in the water when you touch it with a stick, it may be cyanobacteria. If the algae attache to the stick, it is something other than cyanobacteria. In a glass of water, cyanobacteria rise to the surface as tiny greenish particles within about an hour.


Algae bloom risk analysis

Information about algae situation 


You can monitor the cyanobacterial situation via satellite observations through the TARKKA service. Observations are collected daily in the service from both sea and lake areas.

More information

(Telephone 1.00 - 3.00 pm)


  • University Intern Jere Laine, Suomen ympäristökeskus SYKE, Tel. +358 295 252 193,  

Sea areas  

Coastal cyanobacterial observations compiled by

  • University Intern Lilja Nikula, Finnish Environment Institute SYKE, Tel. +358 295 251 209, 

Offshore cyanobacterial observations

  • Reseacher Sakari Väkevä, Finnish Environment Institute SYKE, Tel. +358 295 252 088 (until 6 August)

State of the Baltic Sea

  • Research Manager Samuli Korpinen, Suomen ympäristökeskus SYKE, Tel. +358 295 251 811, (until 30 July)

  • Special Researcher Seppo Knuuttila, Finnish Environment Institute SYKE, Tel. +358 295 251 286, (from 2 August)


  • Communications Intern Sofia Patama, Finnish Environment Institute SYKE, Tel. +358 295 252 245, (until 30 July)
  • Communications Intern Venla Valtanen, Finnish Environment Institute SYKE, Tel. +358 295 251 194, (from 2 August)