Baltic Sea algae Photo: Samuli Korpinen/Eurotrophication
Authorities in Poland this week banned swimming at over 50 beaches along its Baltic coast after hot weather led to the toxic growth of bacteria as  water temperatures exceeded 23 degrees Celsius.  The Baltic Sea has not seen such intense growth of cyanobacteria for 12 years

Holidaymakers were told not to enter the sea, where thick green-brown cyanobacteria colonies have grown and pose a health threat.

Authorities issued warnings that contact with the bacteria may cause allergies and rashes and drinking contaminated water can also lead to serious digestive problems.
A similar ban has been issued for some inland lakes and reservoirs, such as the Zegrze Reservoir near Warsaw.

In neighbouring Germany, authorities issued a warning about the higher than usual growth of vibrio bacteria in the warm Baltic, which can cause deadly illness in people with compromised immune systems. They warned elderly people and those with chronic illnesses such as diabetes or HIV to avoid contact with the sea or brackish water.

In Finland, the Loviisa nuclear power plant reduced energy production in both its units Wednesday to prevent the Baltic Sea water that cools its infrastructure from getting too warm.