The most visible problem of the Baltic Sea is eutrophication that can be observed in summer time as massive algal blooming.
The eutrophication process is well-known, and in the Baltic Sea it started already in the 1800’s. A lot has been done to recover the sea, but the already started eutrophication process is hard to curb.
The effects and synergistic effects of various hazardous substances are less obvious and less known. The concern for these chemicals arose only a few decades ago. We do not have yet enough data to thoroughly evaluate their concentrations in waterbodies or the effects on aquatic ecosystems and human beings.