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Toxic blue-green algae may spread soon, researchers warn

Children and pets must not be allowed into contaminated water, and adults should also avoid swimming, says the Finnish Environment Institute (Syke).

Researchers expect higher concentrations of toxic blue-green algae this summer than usual, spurred by continued warm, calm conditions.

The record-breaking hot weather so far this summer has warmed coastal and inland waters. This creates favourable conditions for cyanobacterial growth, which can be harmful to people and animals.

Satellite images of maritime areas have shown some blue-green algal deposits, and there have also been observations at inland water testing points.

On the other hand, winds have mixed the sea surface water, breaking up algal rafts. This was documented by Border Guard maritime surveillance aircraft flying over southern sea districts on Friday. No large blue-green algae deposits were found in the Gulf of Finland or the Archipelago Sea.

The Finnish Environment Institute (Syke) reported on Thursday that cyanobacteria have been observed in offshore areas throughout the main basin of the Baltic Sea up to the southern and western coasts of the autonomous Åland Islands.

In the open sea areas of the Gulf of Finland, cyanobacteria are present in the upper layer of the water mass over a large area as far as Gogland (Suursaari) in the eastern Baltic.

If the weather stays calm and warm, cyanobacteria may rise to the surface layer. Individual surface algae observations have been made in open sea areas of the eastern Gulf of Finland, north of the islands of Lavansaari, Peninsaari and Seiskari.

"I'm sorry to say, but we're heading in a worse direction all the time," Syke senior scientist Mika Raateoja told Yle.

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Turun Ispoisten uimaranta
The water was still fine for swimming on Friday at Turku's Ispoinen beach. Image: Markku Sandell / Yle

Summer heated up quickly

Compared to recent years, we are a couple of weeks ahead of the usual schedule due to water warming. Raateoja estimates that the algae situation will worsen during July, depending on weather conditions.

In inland waters, the algal situation is still normal although lake surface temperatures are above average.

The last summer with heavy blue-green algae blooms was 2018, when the highest recorded temperature on the open Baltic ever was measured: 27 degrees Celsius.

Raateoja declines to speculate as to whether this summer will turn out to be as bad or worse.

"Blue-green algae is a bit like holidaymakers, meaning the warmer the water, the more comfortable it is to be there," he said. Cyanobacteria is also accelerated by eutrophication due to nutrient pollution caused by humans, including fertiliser run-off from farms.

In the Archipelago Sea, cyanobacteria have been observed in places on the surface, especially in the sea areas north of Nauvo and Korpo and in the Gullkronanselkä area in the western part of the Turku archipelago. Surface algae is also present elsewhere in the archipelago.

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Turun Ispoisten uimaranta
Signs on public beaches usually warn of toxic algae. Image: Markku Sandell / Yle

According to Janne Suomela, Chief Specialist at the Southwest Finland Centre for Economic Development, Transport and the Environment (Ely), there is more blue-green algae in the Archipelago Sea than average at this point in July.

"This is due to the fact that the waters are now record warm, which has enabled blue-green algae to grow and multiply faster," he said.

Abundant algal deposits have been observed in the Archipelago Sea this week near the island of Seili, part of the municipality of Pargas.

According to the Finnish Meteorological Institute, sea surface temperatures are 13–17 degrees Celsius in the Bay of Bothnia, 11–17 degrees in the Bothnian Sea, 17–21 degrees in the Archipelago Sea and 17–21 degrees in the Gulf of Finland.

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sinilevää Seilin saaren rannassa Paraisilla
Algal deposits have been observed this week near the island of Seili. Image: Jari Hänninen / Turun yliopisto

Keep kids and pets out of contaminated water

Syke says that the Baltic Sea has on average warmed by almost two degrees Celsius since 1990 due to climate change, while Finnish sea areas have warmed even more than that.

According to Suomela, there are now good conditions for the strong cyanobacteria blooming due to the exceptional warmth of the water, and calm and warm weather is forecast for next week, which will raise the algae to the surface.

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Sinilevää kelluu rihmoina rantavedessä.
Blue-green algae is often mingled in the water as small particles, which rise to the surface in calm weather. Image: Ari Haimakainen / Yle

For holidaymakers, the blue-green algae forecast does not bode well for swimming opportunities, as it is not advisable to swim in waters with blue-green algae, which can be particularly harmful to children and pets.

"If you see greenish or yellowish particles in the water, or if the algae has accumulated into streaks or larger rafts, think twice before going swimming," Suomela said.

According to Syke, children and pets must not be allowed into contaminated water, and adults should also avoid swimming. Any child or pet suspected of having been exposed to contaminated water should be thoroughly washed with clean water, the institute advises.

Water containing blue-green algae must also not be consumed by people or animals, even after boiling.

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