The Baltic Sea is almost completely enclosed and – except for a few areas – shallow. Its waters are renewed very slowly. Its north and northeast extremities are frozen over for part of the year, and salinity levels there are very low. As a result, the marine environment is very vulnerable, particularly to eutrophication – a build-up of nutrients from urban waste water, coastal agriculture, industrial pollution and atmospheric deposition.
Following the end of the Cold War, shipping and trading have resumed in the Baltic on a large scale; passenger and goods transport is now the main economic activity.