Poland is a signatory of the Helsinki Convention for protection of the Baltic Sea. As a part of this convention, Poland takes part in the International Program for Monitoring the Baltic Sea. From reports prepared as a result of this monitoring it has become apparent that significant amounts of alimentary and toxic substances have flowed from the territory of the country, especially from the Oder and Vistula rivers, into the Baltic Sea, influencing its ecosystems.
In the years 1991–1995, the following pollutants were dumped into the Baltic Sea from the territory of Poland:
– 220 to 280 thousand tons of BZT₅ indicator
– 124 to 247 thousand tons of nitrogen
– 12 to 15 thousand tons of phosphorus
– heavy metals, pesticides and their metabolites.

The high concentration of phosphates and nitrates in the Gulf of Gdansk, the Pomeranian Bay and river mouths along the central part of the coast, lead to eutrophication of the Polish economic zone of the Baltic Sea. The especially visible symptom of this eutrophication in the Gulf of Gdansk and in Szczecin Bay, is the unusually high number of fitoplankton (concentration of alpha-chlorophyll and the amount of primary energy) in the year 1995, as compared to earlier years.

The noted increase of production does not cause negative changes in oxygen availability within the deep sea. The seasonal changes of oxygen concentration, in 1995, as noted in the surface waters in the Gdansk Deep, the southern part of the Gotland Basin and the Bornholm Deep, have not changed significantly since 1990.

The presence of oxygen in the deep layers has deteriorated in 1995, with respect to the beginning of the 1990’s. The deficit of oxygen and the increase in sulphuretted hydrogen concentration is, in greater part, a result of the isolation of these deep layers from contact with surface waters, and not from Eutrophication. This also results in an increase in the concentration gradient of haloclines, which is a direct result of the drainage of salt waters in 1993 and 1994.

The current level of Eutrophication is not yet hazardous to the biodiverstiy in the Polish zone of the Baltic Sea. In 1995, no significant changes in the species composition of fitoplankton, zooplankton and zoobenthose were noted, in comparison to previous years.
The frequent periods of high oxygenation of waters and the increase in sulpheretted hydrogen concentration negatively influence the zoobenthose and fish living on the sea floor. This results in apparent negative economic repercussions. In Kattegat, the border of the commercial fishing area moved further north. In Bornholm, Gdansk, and Gotland Basins the traditional cod spawning grounds were destroyed.

Analysis which confirmed the amounts of heavy metals, pesticides, as well as the metabolisms of fish were performed as a part of the Baltic monitoring program, in effect since 1979. The research illuminates the significant differentiation of contents of these substances with respect to the type of fish and fishing region. The highest concentration of toxic substances was found in fish which inhabit the drainage areas of larger Polish rivers. In the years 1979–88, a decrease in the concentration of mercury, cadmium, lead, DDT, zinc and PCB was observed. Since 1992, toxic substance research was limited to the fish which come from the Darlowski-Kolobrzeski fishery. The results of the research performed in 1995 indicate that the amount of toxic substances in the cells of the fish varied for many years.
Graphs A and B illustrating Average Amounts of Toxic Substances in Herring Cells (Clupea harengus) from the Kolobrzeski-Darlowski Fishery in the Years 1992–1995 (according to “State of Cleanliness of Rivers, Lakes, and the Baltic Sea: based on the results of the national environment monitoring system in 1994–1995”, PIOS Environmental Monitoring Library – Warsaw 1996).

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