Suomen ympäristökeskus

Earlier-than-usual observations of blue-green algae in marine areas, situation in inland waters typical for early summer


The warm weather in early summer and early warming of the sea water brought forward blue-green algae observations in the offshore areas of the Gulf of Finland. This week has seen an increase in occurrences of surface algae along the Gulf of Finland coast. In inland waters, there has been a slight increase in blue-green algae observations since last week, but the situation is typically calm for early summer.

Alt text: "Satellite image showing surface algae blooms in the coastal area between Porvoo and Kotka, taken on 18 June 2024."
The satellite image shows the occurrences of surface algae observed in the coastal area between Porvoo and Kotka on 18 June 2024. USGS/NASA Landsat Program, Syke (18.6.2024)
To view this piece of content from, please give your consent at the top of this page.

Link to the map

Map of the national blue-green algae monitoring observations on week 25

More in Finnish

Merialueiden sinilevähavainnot aikaistuneet, sisävesillä tilanne alkukesälle tyypillinen.

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 20 June to 8 August 2024. 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. 




Valtteri Toikka,, Tel. +358 295 251 364

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:

Media service at Finnish Environment Institute

Our Media Service provides information on research, helps journalists find experts for interviews and provides photos for media use.

Our Communication experts will answer your inquiries on weekdays from 9 am to 4 pm.

Tel:+358 295 251


Alt text: "Satellite image showing surface algae blooms in the coastal area between Porvoo and Kotka, taken on 18 June 2024."
The satellite image shows the occurrences of surface algae observed in the coastal area between Porvoo and Kotka on 18 June 2024.


Finnish Environment Institute - We build hope through research.

Finnish Environment Institute
Latokartanonkaari 11
00790 Helsinki

+358 295 251 000

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.

Subscribe to releases from Suomen ympäristökeskus

Subscribe to all the latest releases from Suomen ympäristökeskus by registering your e-mail address below. You can unsubscribe at any time.

Latest releases from Suomen ympäristökeskus

Observationerna av cyanobakterier har ökat något i insjöarna11.7.2024 14:50:43 EEST | Tiedote

Observationerna av cyanobakterier har ökat något i insjöarna i hela landet och observationer har gjorts ända till Lappland. På öppet hav finns det nu cyanobakterier i Finska viken och Skärgårdshavet, i södra Bottenhavet håller cyanobakterier på att utvecklas. I kustområdet har cyanobakterier fortfarande observerats huvudsakligen vid Nylands och Egentliga Finlands kuster och antalet observationer har knappt förändrats alls.

Slight increase in blue-green algae observations in inland waters11.7.2024 14:40:48 EEST | Press release

Blue-green algae observations have increased slightly throughout the country, and observations have been made even in Lapland. Blue-green algae now occur in the Gulf of Finland and the Archipelago Sea. In the southern part of the Bothnian Sea blue-green algae are just developing. Blue-green algae have still been observed in the coastal area, mainly on the coasts of Uusimaa and Southwest Finland, and the number of observations has not changed much.

Sinilevähavainnot sisävesillä lisääntyneet hieman11.7.2024 13:00:00 EEST | Tiedote

Sinilevähavainnot ovat hieman lisääntyneet sisävesillä koko maassa, ja havaintoja on tehty aina Lappia myöten. Avomerellä sinilevää on nyt Suomenlahdella ja Saaristomerellä, Selkämeren eteläosassa sinilevä on vasta kehittymässä. Rannikkoalueella sinilevää on havaittu edelleen pääasiassa Uudenmaan ja Varsinais-Suomen rannikolla, eikä havaintojen määrä ole juurikaan muuttunut. Huom! Korjattu tiedotteen lopussa: Kuluvalla viikolla Järvi-meriwikin ja kautta saatiin enemmän kansalaishavaintoja kuin viime viikolla.

The blue-green algae situation has remained stable since last week, unstable and windy weather slows down the growth of blue-green algae4.7.2024 13:06:23 EEST | Press release

The blue-green algae situation has remained stable since last week. In inland waters, blue-green algae observations have slightly decreased, and the algae situation in coastal areas has remained unchanged. In sea areas, windy weather has largely mixed blue-green algae with water mass. In recent days, blue-green algae have been observed especially in the west of Hanko and the Upinniemi open sea area.

Algläget har hållits stabilt sedan förra veckan, det instabila och blåsiga vädret dämpar ökningen av cyanobakterier4.7.2024 13:03:26 EEST | Tiedote

Algläget har varit stabilt sedan förra veckan. Observationerna av cyanobakterier har minskat något i insjöarna och algläget i kustområdena har förblivit oförändrat. I havsområdena har det blåsiga vädret till stor del blandat ihop cyanobakterierna med vattenmassan. Under de senaste dagarna har cyanobakterier observerats särskilt väster om Hangö och i Obbnäsfjärden.

In our pressroom you can read all our latest releases, find our press contacts, images, documents and other relevant information about us.

Visit our pressroom
HiddenA line styled icon from Orion Icon Library.Eye