WARSAW - Polish health authorities said Wednesday they had closed scores of beaches along the country's Baltic Sea coast due to a massive toxic algae bloom triggered by a heat wave.
"Swimming is prohibited on eight beaches along the open sea and about twenty beaches in Gdansk Bay because of the appearance... of cyanobacteria," Tomasz Augustyniak, health inspector for the northern Gdansk province, told AFP referring to blue-green algae.
"The algae is toxic and poses a health risk," he said, adding that the week-old bloom was "particularly intense" due to a long stretch of hot weather.
Polish television this week broadcast aerial footage showing a green carpet of algae covering the sea.
Run-off containing nitrates and phosphates from farm fertilizers and sewage have seeped into the Baltic, triggering large algal blooms in recent years, Augustyniak said.
Dying algae also triggers complex organic processes that suck the oxygen out Baltic waters leading to "dead zones" where no marine life can exist.
Scientists termed oxygen loss in the Baltic "unprecedently severe" in a study published this month in the European Geosciences Union journal Biogeosciences.
They note that as a relatively small, shallow and enclosed sea, the Baltic has a very limited ability to flush out pollutants into the waters of the North Sea, making it an extremely vulnerable ecosystem.
Encircled by nine countries -- Estonia, Denmark, Finland, Germany, Latvia, Lithuania, Poland, Russia and Sweden -- the Baltic has an estimated 16 million people living along its shores, the AFP news agency points out.