Radio | News week in plain Finnish | Saturday 12.7.2025

Amount of blue-green algae

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The topic of the week is blue-green algae.

There has been relatively little blue-green algae in the lakes this summer. However, heat can increase blue-green algae quickly.

Blue-green algae can produce toxins. You should not swim in the water or drink it.

Let’s talk more about it now.

Amount of blue-green algae

Man sunbathing on the beach. The pictures were taken at the Emmännä beach in Oulu.

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A man sunbathes on a beach in Oulu on July 10, 2025. Photo: Janne Körkkö / Yle

There is still quite a bit of blue-green algae observed in the lakes. This week there was even less blue-green algae in some places than last week.

On Thursday, there was a lot of blue-green algae in only four places.

The Finnish Environment Institute monitors the amount of blue-green algae in lakes, on the coast and at sea.

The amount of blue-green algae in the sea has increased slightly. The amount can be seen from satellite images.

Algae appears as green or yellow rafts in the water.

Weather affects blue-green algae

Blue-green algae on the beach next to the pier.

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Blue-green algae in Emäsalo, Porvoo, in the summer of 2024. Photo: Mikael Kokkola / Yle

There is less blue-green algae now than usual in the middle of summer.

There is little algae because the weather has been quite cool.

The lake water temperature was mostly below 20 degrees Celsius at the end of the week, meaning the water is colder than usual in July.

However, the amount of blue-green algae can increase rapidly when the weather warms up. The heat quickly warms the water surface and a blue-green algae bloom can begin.

Blue-green algae grow easily in warm, nutrient-rich water that is not disturbed by wind. Blue-green algae are usually found where there are people and agriculture.

Toxic blue-green algae

Image of a sign on the beach warning about blue-green algae. The sign says that swimming is not recommended.

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Warning sign about blue-green algae in Kotka in summer 2021. Photo: Jasmina Kauta / Yle

The growth of blue-green algae is monitored because blue-green algae can be toxic.

You should not swim in the water if it contains blue-green algae. You should also not drink the water and it should not be used for washing.

Blue-green algae can cause breathing difficulties, rashes, and stomach pain, among other things. The toxin affects humans and animals.

You can check the amount of blue-green algae on the Finnish Environment Institute website. You can also report your own observations of blue-green algae on the website.

Repetition

![Blue-green algae of the lake on the beach.](https://images.cdn.yle.fi/image/upload/c_crop,h_3375,w_6000,x_0,y_309/ar_1.7777777777777777, c_fill,g_faces,h_431,w_767/dpr_1.0/q_auto:eco/f_auto/fl_lossy/v1559816679/14-svyle-134491531974aae73dd)

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Blue-green algae on the shore of a lake. Photo: YLE/ Lone Widestam

In the news week, we reported on the amount of blue-green algae.

There has been relatively little blue-green algae in the lakes this summer. However, warming weather could increase the amount of blue-green algae rapidly.

Blue-green algae can produce toxins. You cannot swim in the water and you should not drink the water.