The environmental quality of the Baltic Sea is largely influenced by the inputs of pollutants - particularly excessive nutrients, and hazardous substances.
Nutrients can enter the sea in runoff from arable land, mainly via rivers and streams, but also along coasts; or in the form of deposition from the air.
The main pathways of hazardous substances to the marine environment are industrial and municipal wastewater, and atmospheric deposition, but also leachate from deteriorating stockpiles, as in the case of obsolete pesticides.
More than 25 of the 132 serious pollution hot spots identified around the Baltic Sea since 1992 have already been cleaned up.
The impact of less localised, diffuse sources of pollution is nowadays becoming more crucial and is difficult to control.
Pollution means introduction by man, directly or indirectly, of substances or energy into the sea, including estuaries, which are liable to create hazards to human health, to harm living resources and marine ecosystems, to cause hindrance to legitimate uses of the sea including fishing, to impair the quality for use of sea water, and to lead to a reduction of amenities.