Summary of the national cyanobacteria review June–August 2022: Abundant cyanobacteria observed at sea this summer, cyanobacterial situation in lakes remained at the level of recent years

Press release 2022-08-25 at 15:55
Laivalta otettu kuva, jossa näkyy sinilevää
SYKE's marine research vessel Aranda observed cyanobacteria in the northern part of the Baltic Proper on 9 August 2022. © Sirpa Lehtinen / SYKE

The cyanobacterial situation in the past summer has varied according to changing weather conditions. Cyanobacterial levels in sea areas and lakes peaked during the hottest periods of the summer in mid-July and mid-August. The cooler weather in late July and early August curbed the growth of cyanobacterial blooms for a while. In lakes, this summer’s cyanobacterial situation remained quite typical compared to previous years. However, regional variation has been high, and the most abundant observations made in the national cyanobacterial monitoring were centred in a few nutrient-rich lakes. The cyanobacterial bloom risk analysis was realised and abundant cyanobacteria were observed, especially in the southwestern, southern and western sea areas. In the week that began on 22 August, there have still been quite abundant cyanobacteria at sea and in lakes.

Variable cyanobacteria summer in lakes

During the summer, the cyanobacterial situation in lakes has varied with the weather. In the early summer, cool weather curbed the formation of cyanobacterial blooms, and the cyanobacterial situation was characteristic of the time of year. After the warming of the weather after Midsummer, cyanobacterial blooms became more abundant in many places. The cooler weather in late July lowered the surface temperature of lakes and weakened the cyanobacterial blooms. As a result of winds, the cyanobacteria also remained mixed with the surface waters. At the beginning of August, warm weather raised the temperature of surface waters by several degrees in the whole country. In addition to this, strong winds and rainfall brought nutrients from the lakebeds and the catchment area, and so cyanobacterial blooms became again more abundant almost throughout the country.

The cyanobacterial situation in lakes has been subject to great regional and local variation during the summer. In the regions of Uusimaa, Southwest Finland and Kainuu, the summer’s cyanobacterial situation has been in line with the long-term average throughout the summer. In the rest of the country, the cyanobacterial situation has fluctuated between both sides of the long-term average. The peak of cyanobacterial blooms was reached during the August heat wave, with the exception of Lapland.

This summer, the nationwide algal monitoring in lakes included about 275 sites. During the summer, cyanobacteria were observed at 138 sites, which is roughly the same number as in the previous summer. Some cyanobacteria were found at 100 sites, abundant occurrences at 68 sites and very abundant at only four sites.

cyanobacterial blooms occur in eutrophic lakes where phosphate phosphorus nutrients are abundant. In the most eutrophic lakes, cyanobacterial blooms have lasted for several weeks this summer. In other lakes, cyanobacterial blooms may have lasted only for two to three weeks or less,” says Senior Research Scientist Kristiina Vuorio from the Finnish Environment Institute.

Towards the end of August, cyanobacterial blooms have become more abundant in some places. Very abundant cyanobacterial blooms have not been observed during the past week. Abundant cyanobacteria were observed at 14 monitoring sites and some cyanobacteria at 38 sites. At the end of the summer holiday period, the number of cyanobacterial observations received from citizens has clearly decreased. In the last seven days, only 50 observations have been received through the observation courier service and the map service, 26 of which have been observations that included cyanobacteria.

Abundant cyanobacteria were observed during the summer in the southwestern, southern and western sea areas

In Finnish sea areas, the amounts of cyanobacteria began to increase already at the turn of June and July as a result of the hot weather. The number of cyanobacterial observations peaked for a couple of weeks in mid-July and again around mid-August. Between these periods, cyanobacterial observations decreased momentarily due to the cooling weather. The amounts of cyanobacteria are still unusually high in late August, and if the weather and nutrient conditions continue to be favourable, cyanobacteria may occur in many areas well into autumn.

When seen nationally, cyanobacteria were on average more prevalent at coastal and archipelago algal observation sites during the peaks of June–August than during the corresponding periods in 1998–2021. However, comparisons with previous years are only indicative, as the number and location of observation sites have varied over the years. Most of the coastal observations were made in the Archipelago Sea, the western Gulf of Finland and the Bothnian Sea, but cyanobacteria also occurred in other coastal areas. On the coasts and in archipelagos, the amounts of cyanobacteria vary rapidly and the cyanobacterial situation can be very different in places very close to each other.

In the open sea areas near Finland, cyanobacteria were observed especially in the northern part of the Baltic Proper, south of Åland and the Archipelago Sea, in the Gulf of Finland from Gogland to the Archipelago Sea and in the Bothnian Sea as far up as Kvarken. There have been less cyanobacteria in the eastern parts of the Gulf of Finland than in the western parts, but at the end of August, abundant cyanobacteria have been observed in some inlets in the eastern Gulf of Finland.

“Based on observations from the marine research vessel Aranda and Utö atmospheric and marine observation station, there were three species of cyanobacteria in the occurrences. Nodularia spumigena, Aphanizomenon flosaquae and Dolichospermum spp. were found in varying quantities in all samples. However, Nodularia spumigena was more abundant in the Gulf of Finland and the Bothnian Sea than in recent years”, says Senior Research Scientist Sirpa Lehtinen from SYKE.

There are differences between different species in their ecological characteristics and, among other things, in their production of harmful compounds. Nodularia spumigena has so far always been found to be toxic. Other species of cyanobacteria may also produce various liver and nerve toxins and other compounds that are harmful to health and may cause allergic symptoms. Cyanobacterial blooms should therefore always be treated with caution as they may pose a health hazard to humans and domestic animals.

“In the future, we want to investigate in more detail the species composition of cyanobacterial occurrences with satellite observations. We already use observations from six different satellites in our daily monitoring, so it’s possible to do a combined analysis of cyanobacteria species data and satellite observations from measurement voyages,” says Senior Scientist Jenni Attila from SYKE.

In the last week towards the end of August, 19 cyanobacterial observations have been made in coastal and archipelago areas, mainly in the Archipelago Sea. In the Gulf of Finland and around Kvarken, cyanobacteria have also been observed on the open sea. On the open sea, cyanobacteria rise to the surface especially when degraded cyanobacterial cells have lost their ability to regulate their position in the water column.

The cyanobacterial bloom risk analysis was realised

The cyanobacterial bloom risk analysis made at the beginning of June was mainly based on the nutritional situation during the winter, as the summer’s weather conditions cannot be predicted. The availability of phosphorus nutrients for cyanobacteria was predicted to be high, and therefore the risk of cyanobacterial blooms was estimated to be high. This summer, growth conditions have remained favourable for cyanobacteria, as warm weather and the mixing of water that brings phosphorus nutrients into surface waters have alternated. This summer's bloom risk has largely been realised in the areas suggested in the cyanobacterial forecast.

However, there is a need for more understanding of the growth potential of cyanobacteria in the Bothnian Sea, as cyanobacterial blooms have been more abundant and extensive this summer than the winter’s nutritional situation would have suggested. In addition, the presence of Nodularia spumigena in the northern part of the Bothnian Sea indicates a change in the Bothnian Sea ecosystem. Cyanobacteria observations in the Kvarken area have increased alarmingly in recent years.

“On the basis of cyanobacterial blooms during a single year, no conclusions can be drawn about the development of the state of the Baltic Sea. Therefore, regular monitoring of species and water quality is necessary. The nutritional situation continues to favour cyanobacterial blooms in large areas of the Baltic Sea. For this reason, the cyanobacterial situation in areas with the biggest bloom risk is primarily determined by the summer's weather conditions,” says Senior Research Scientist Jouni Lehtoranta from SYKE.

Cyanobacterial observations 2022
Summary of cyanobacterial observations recorded in the Järvi-meriwiki online service during June–August and of the summer surface algae areas interpreted on the basis of satellite observations. The summary compiles the cyanobacterial observations made during the summer in different regions so that the most abundant individual observations are presented at the top. Cyanobacteria observations: Järvi-meriwiki online service, national cyanobacterial monitoring and SYKE satellite observations. The colour scales of the satellite observations and the observation classification in Järvi-meriwiki correspond to each other. © Contains modified Copernicus and USGS/NASA Landsat Program data, SYKE (2022)

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

The Finnish Environment Institute (SYKE) monitors the cyanobacteria occurrences as part of the monitoring of the state of the environment and has published a weekly overview of the cyanobacterial situation in inland waters and sea areas near Finland in June–August. Cyanobacterial observations will continue until the end of September, but the publication of weekly national overviews will end at the end of August.

The typical time for cyanobacterial blooms is from the turn of June and July until August. In late summer, the cool nights tend to lower the water surface temperatures, which can curb the occurrence of cyanobacterial blooms. Reduced light levels also curb the growth of cyanobacteria. However, abundant cyanobacterial blooms may still occur in September and weak blooms even in October–November. If cyanobacteria have sufficient nutrients, they can continue to bloom under the ice cover. The phycocyanin dye pigment released from degrading cyanobacterial cells can dye water and beaches and, in winter, ice slices to turquoise or bluish and form a turquoise paint-like mass on beaches.

Nationwide cyanobacterial monitoring has been carried out since 1998. The monitoring is the result of cooperation between SYKE and the Centres for Economic Development, Transport and the Environment (ELY Centres) and municipal environmental authorities. Rotary Finland has also been involved in the monitoring for three years now. The monitoring includes over 400 permanent observation sites around the country in inland waters and coastal areas and in the archipelago. Individual citizens can participate in the monitoring by sending their observations via the smartphone-friendly Havaintolähetti website to the Järvi-meriwiki online service or through the cyanobacterial situation map service on the website.

Information on the cyanobacterial situation in the sea areas near Finland was gathered from satellite images, the Finnish Border Guard, marine research vessel Aranda, the species, biomass, and pigment results of cyanobacteria at the Utö Atmospheric and Marine Research Station, and cruise and merchant ships equipped with Alg@line measuring equipment. The seagoing service of the Finnish Meteorological Institute provided up-to-date information on sea surface temperatures, and the drift forecasts for cyanobacterial rafts were also prepared in cooperation with the Finnish Meteorological Institute. This year, satellite observations were utilised not only in sea areas but also in 50 lake areas.

More detailed information on the local cyanobacterial situation is available from the ELY Centres, municipalities and cities. If poisoning is suspected, contact the Poison Information Center, a doctor or veterinarian.

SYKE thanks all parties involved in cyanobacterial monitoring for their important cooperation!

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.

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.

Cyanobacterial observations also in the Itä 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.

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.

Algae bloom risk analysis

Information about algae situation 

Satellite observations

Utö atmospheric and marine observation station and Alg@line monitoring

Networks for marine research

Map images for media use

More information

(Telephone 1 pm to 3 pm)


  • Senior Research Scientist Kristiina Vuorio, Finnish Environment Institute SYKE, tel. 295 251 757,

Sea areas  

Coastal cyanobacterial observations

  • Senior Researcher Sirpa Lehtinen, Finnish Environment Institute SYKE, Tel. 0295 251 353,

Offshore cyanobacterial observations

  • Leading Researcher Jenni Attila, Finnish Environment Institute SYKE, Tel. 0295 251 078,

State of the Baltic Sea

  • Research Professor Markku Viitasalo, Finnish Environment Institute SYKE, Tel. 0295 251 742,


  • Communications Intern Vilma Ruponen, Finnish Environment Institute SYKE, Tel. 0295 251 039,

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