Blue-green algae reports rise to nearly 260 in Finland

Blue-green algae sightings in Finland increased last week, with nearly 260 observations reported across inland waters and coastal areas, according to the national monitoring system.

The rise follows a period of rain and warm weather in early July, which has promoted algae growth in many locations. Strong winds, however, have disrupted the formation of surface blooms by mixing the algae into the water.

Inland waters accounted for 203 observations this week. While no extreme blooms were recorded, significant algae presence was noted in Rokuanjärvi (Vaala), Savijärvi (Sipoo), Kirkkojärvi (Naantali), and Haapajärvi (Lappeenranta). Trace amounts were detected at 22 other sites, stretching as far north as southern Lapland.

Coastal areas saw 55 observations, an increase from the previous week but still below typical levels for this time of year. The highest concentrations were reported off Kotka in the Gulf of Finland, at Genböle beach in Kemiönsaari, Kärmäläiset in Naantali, and Hökberg in Pargas. Ten other coastal sites, including parts of the Archipelago Sea and Bothnian Sea, reported minor algae presence.

An additional 139 public reports were submitted via the Järvi-meriwiki and Vesi.fi platforms, with 71 confirming blue-green algae sightings.

Offshore conditions are monitored using satellite-based algae barometers, which estimate bloom probability in Finland’s nearby sea areas. The barometers, published by the Finnish Environment Institute, allow comparisons with previous years. Cloud cover in early July has limited satellite detection, but available data suggest algae are also increasing in the Bothnian Sea.

Weekly monitoring covers around 300 observation points and will continue until the end of September.