“We’re seeing a whole load of algae down in the water and in certain places it has risen to the surface,” said pilot Leif Snäckerström.
The noxious cyanobacteria, as the algae is technically known, now stretches from Landsort, off the coast near Nynäshamn, up to Singö in the northern Stockholm archipelago, according to Aftonbladet.
“In the area east of Runmarö there’s a great deal of algae,” Gunnar Aneer, a marine biologist at Stockholm council, told the paper.
“If you can’t see the bottom when the water’s half a metre deep, don’t go swimming,” he advised.
The annual outbreak of algae, caused by high levels of phosphorous in the Baltic, has ruined many a Swede’s coastal holiday in recent years. But apart from the stench and the unpleasant appearance, the algae can be hazardous.
While human bathers can experience stomach cramps, headaches and rashes after swallowing the algae, it can be fatal for dogs.
The relatively cool and cloudy summer has meant that the levels of algae this year have not been as high as in 2005 and 2006.