WARSAW, Poland (AP) — Thinking of a dip in the Baltic Sea to cool off from the unusually scorching European summer? It's too hot for that.

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 in the unusually warm sea. Baltic Sea water temperatures exceeded 23 degrees Celsius (73.4F) in some places Thursday.

Emergency water rescuers told vacationers on hot sandy beaches — from Swinoujscie in the west to Gdynia in the east — not to enter the sea, where thick green-brown cyanobacteria colonies have grown and pose a health threat.

Regional sanitation authorities have issued warnings that contact with the bacteria may cause allergies and rashes. Drinking contaminated water can also lead to serious digestive problems.

The Baltic Sea has not seen such intense growth of cyanobacteria for 12 years. It results from exceptionally high air temperatures of 34 degrees Celsius (93.2 degrees Fahrenheit) that have raised the temperatures of the usually cold Baltic.

A similar ban has been issued for some inland lakes and reservoirs, such as the Zegrze Resevoir near Warsaw.

In neighboring Germany, authorities issued a warning about the higher than usual growth of vibrio bacteria in the warm Baltic that can cause deadly illness in people with compromised immune systems. They said a 70-year-old man with a chronic illness died of vibrio infection over the weekend, and 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 said in a statement it briefly reduced energy production in both its units Wednesday to prevent the Baltic Sea water that cools its infrastructure from getting too warm. It said there was no danger to people or the environment.