The Baltic Sea is a sea of the Atlantic Ocean, extending eastward from the North Sea, and surrounded by Denmark, Germany, Poland, Lithuania, Latvia, Estonia, Russia, Finland and Sweden. It includes the Gulf of Finland, the Gulf of Bothnia and the Kattegut. Though there is little water exchange between the Baltic and the Atlantic; the Baltic Sea drains through the Danish islands into the Kattegat and the Skagerrak and into the North Sea. Water in the northern and eastern parts of the Baltic is brackish, of considerably lower salinity than the waters of the Atlantic. As a result, there is a mixture of freshwater and marine species in the Baltic. The southern shore of the Baltic is characterized by wide coastal dunes. Historically the countries around the shores have vied for control of shipping. For over 400 years the Hanseatic League played a major role in shaping economies, trade and politics in the North Sea and Baltic Sea. the League came to dominate Baltic maritime trade for three centuries along the coast of Northern Europe. It stretched from the Baltic to the North Sea and inland during the Late Middle Ages and early modern period. During World War II, the German Navy controlled the Baltic to keep the Russian Navy contained. Strategically this continues to be a bottleneck for Russian ships.