Cyanobacterial blooms observed at only one observation site in the Finnish sea areas, a few observations in lakes.

Press release 2021-06-03 at 15:14
Pollen in Lake Vesijärvi in Lahti 1 June 2021. © Anna-Elina Lehtinen

The Finnish Environment Institute (SYKE) has started reporting observations of summer 2021 cyanobacteria blooms this week. Some cyanobacteria has been observed at one observation site in the eastern part of the Gulf of Finland. So far, only three observations of cyanobacteria have been made in the lakes. There may be yellow pollen in the coastal waters that can look deceptively like cyanobacterial blooms. The Finnish Environment Institute reports on the national cyanobacterial situation on a weekly basis until the end of August. The ELY centres (Centre for Economic Development, Transport and the Environment) provide more detailed information on the cyanobacterial situation in their own areas. Municipalities and cities monitor the cyanobacterial situation on the beaches. SYKE has also today published an assessment of the risk of cyanobacterial blooms in the Finnish sea areas for the upcoming summer.

Some cyanobacteria at one observation site in the eastern part of the Gulf of Finland.

There is a normal early summer situation in the Finnish sea areas; in other words, no significant and widespread cyanobacterial blooms have yet been observed. Some cyanobacteria has been observed at one observation site in the eastern part of the Gulf of Finland. No cyanobacterial blooms have been detected in the open seas from satellite images.

“The amount of cyanobacteria in the sea areas near Finland usually only increases in July as the surface temperature of seawater exceeds about 16–17 degrees. The formation of large cyanobacterial rafts usually requires at least a couple of weeks of favourable temperature and wind conditions to develop,” says Sirpa Lehtinen, Senior Research Scientist at the Finnish Environment Institute.

According to the Finnish Meteorological Institute, the sea surface temperature is 4-10 °C in the Bay of Bothnia, 7-11 °C in the Bothnian Sea, 10-13 °C in the Archipelago Sea and 10-12 °C in the Gulf of Finland.

Pollen can form yellowish floating ratfs. However, pollen is usually also found on dry land, for example, on piers and yard furniture.

Only a few cyanobacterial observations in lakes

There is a normal early summer situation in the Finnish lakes; in other words, no cyanobacterial blooms have been observed. Some cyanobacterial blooms have been observed at only three of the national algae observation sites. No abundant or very abundant cyanobacterial surface blooms have been observed in the lakes. In the early summer, conifer pollen can form yellowish floating rafts on the beaches.

”Cyanobacterial blooms occur mainly in eutrophic waters with sufficient phosphorus available for algae growth. In addition to phosphorus and water temperature, the growth and formation of cyanobacterial blooms are affected by many factors, which makes it difficult to assess the development of the cyanobacterial situation on one particular lake in advance,” says Senior Research Scientist Kristiina Vuorio from the Finnish Environment Institute.

Surface blooms are typically formed during warm and calm weather periods. A substantial amount of cyanobacteria usually forms in lakes in July and August, but the warm weather in early summer can advance the growth of cyanobacterial blooms.

The lake surface temperatures are typical for the season. The surface temperature in the lakes of southern and western Finland is generally 14–16 degrees, in the central and eastern parts of the country and in Kainuu usually 11–14 degrees and in northernmost Finland less than 10 degrees. Some of the lakes in Northern Finland are still frozen.

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 

More information

(Telephone 1.00 - 3.00 pm)


  • Senior Research Scientist Kristiina Vuorio, Finnish Environment Institute SYKE, Tel. +358 295 251 757, (until June 4)
  • University Intern Jere Laine, Suomen ympäristökeskus SYKE, Tel. +358 295 252 205,  (from June 7)

Sea areas  

Cyanobacterial bloom situation

  • Senior Research Scientist Sirpa Lehtinen, Finnish Environment Institute SYKE, Tel. +358 295 251 353,  (until June 4)
  • Researcher Heidi Hällfors, Finnish Environment Institute SYKE, Tel. 0295 251 114,  (from June 7)

State of the Baltic Sea

  • Leading Researcher Harri Kuosa Finnish Environment Insitute SYKE, Tel. +358 295 251 106, (until June 4)

  • Senior Researcher Antti Räike, Finnish Environment Institute SYKE, Tel. +358 295 251 586,  (from June 7)


  • Communication Specialist Hannele Ahponen, Finnish Environment Institute SYKE, Tel +358 50 327 5997,