] The Southern Gotland Basin (the Arkona basin) covers the southernmost parts of the Baltic Sea, from the Danish straits to the coast of Lithuania and to southern Sweden.
The water by the Danish straits is saltier than in the Baltic Sea up north, and it is an area where starfish, crab, and many other animals of the oceans thrive, a feat impossible in the colder and less salty waters of the northern marine areas. The southern marine areas of the Baltic Sea are also home to the harbour porpoise, the only whale species that is regularly spotted in the Baltic Sea.
In favourable conditions, the shallow, sandy seabeds are covered by underwater eelgrass meadows. Lagoons, separated from the open sea by narrow sand ridges, are typical on the southern shores: the largest of these is the 100 km long Curonian Spit in front of Lithuania and Kaliningrad.
Poland, located on the southern shore of the Baltic Sea, is the most highly populated of the countries around the Baltic Sea – it is home to almost 40 million people, i.e. half of the entire population of the Baltic Sea catchment area. This is why Poland plays a key role in the wellbeing of the Baltic Sea. Two major rivers, the Vistula and the Oder, flow from Poland to the Baltic Sea, carrying with them great volumes of nutrients from agriculture and the cities. Through the projects of the John Nurminen Foundation, nutrient discharges have been reduced by e.g. improving the efficiency of wastewater treatment in Warsaw, Gdansk, and Szczecin.