The Baltic Sea is a semi-enclosed regional sea in northern Europe with relatively low-saline water due to excess fresh water runoff and a narrow and shallow entrance from the North Sea. Irregular saline inflows cause a salinity stratification that prevents wind mixing and fall convection from ventilating the deepest layers. This unlucky natural design combined with many years of eutrophication has caused a situation with anoxic and hypoxic conditions in the deeper parts of the Baltic Sea and an excess of available phosphorous in the system. This causes good living conditions for nitrogen fixing cyanobacteria.
These form blooms during summertime and are the primary HAB concern of the Baltic Sea. During calm weather, surface scums form and these scums are a nuisance for tourists and others. The toxin may also accumulate in filter feeders such as bivalve molluscs.The impacts of these HABs are primarily a concern for public health, tourism, water supply, and marine ecosystems.
Surface accumulation of cyanobacteria in southern the Baltic Sea. A polarizing filter was used.
Examples of existing relevant services regarding cyanobacteria blooms are the Algae Watch System by SMHI, and AlgAwavare which is a monthly bulletin by SMHI on the observations of harmful algae at the species level.