Blue-green algae – Cyanobacteria
When blue-green algae is observed at a public beach, a notice is put up warning against swimming. If the water is green from algae or if there is an algae blanket on the water surface, you should not bathe in the water. Small children and pets should be kept at a distance from the beach so that they do not swallow water that may contain blue-green algae. Especially on sea beaches, the algae situation can quickly change. Winds and currents can move the algae so that the amount of algae changes quickly during the same day.
The amount of blue-green algae or cyanobacteria generally increases at the end of summer. Small amounts in the water look like pollen-like yellow or green grains. In calm weather, blue-green algae form a veiled, green membrane on the surface of the water. A blue-green algae occurrence may look different depending on the location and amount. An abundant occurrence of blue-green algae colours the water green and resembles green paint or yellow-green pea soup on the water surface or beach. When the algae mass dries, it can assume a blue-green or turquoise colour. Blue-green algae has a musty smell similar to soil or mould.
When checking for the possible presence of blue-green algae, water can be collected in a transparent container and examined against the light. Blue-green algae is seen in the water as greenish flakes or sticks. If you leave the water in the container for a while, the algae will rise to the surface.
Information regarding the algae situation can be found on the joint website of Finland’s environmental administration.