The most affected areas are from Denmark’s Bornholm eastwards to the Bay of Gdansk and north along the eastern Baltic coast to the mouth of the Bay of Finland.
There is also a small area north of Öland, according to the Information Office for the Baltic Proper at the County Administrative Board of Stockholm (Informationscentralen för Egentliga Östersjön vid Länsstyrelsen i Stockholms län).
Certain cyanobacteria produce cyanotoxins, resulting in algal blooms that can be toxic and dangerous to humans and animals. Recent studies suggest that significant exposure to high levels of cyanobacteria causes amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease).
The office reported that the research vessel Argos has found the cyanobacteria Nodularia spumigena east and west of Bornholm on its journey in the Baltic. In the northern Baltic, two cyanobacteria, Aphanizomenon sp. and Anabaena spp., were found in Landsort Deep and outside Askö last week.
“There is a slight tendency for the amount of cyanobacteria in the body of water to be less in the northern part of the Baltic Sea than in the southern part,” wrote Sture Nellbring in a statement.
A high-pressure weather system is expected to reach Scandinavia on Friday which is expected to strengthen over the weekend with sunny conditions and little wind. This means that the risk of surface accumulations will increase, especially in the southern and eastern parts of the Baltic Sea where cyanobacteria blooms have been detected, Nellbring wrote.
The volume of water in the northern Baltic proper has low phosphorus values, which may hinder the bloom. In the southern part of the Baltic Sea, the phosphorus values are normal, resulting in a higher potential for blooming in that area.
“We do not expect strong blooms or surface accumulations in the Swedish coastal areas during the coming weekend,” Nellbring wrote.