Attention: Blue-green algae can develop on Finnish beaches between seasons. It is advisable to ask locals beforehand whether there is blue-green algae. If so, a bath with children or animals is not recommended and a shower for adults is highly recommended. A mass proliferation of cyanobacteria can severely affect water quality and significantly limit water use. The bacteria produce a variety of secondary metabolites that act as allelochemicals, antibiotics, hormones and toxins. B. can harm fish and zooplankton. Some of the toxins are among the most powerful natural gifts and can also be hazardous to the health of humans and land animals. For example, allergic skin reactions and deflations can occur when swimming. If you slick water containing cyanobacteria, it can also cause stomach and intestinal infections.