Geography of Europe is not surrounded by sea and its southeastern border has always been variously defined for centuries. In terms of shape, Europe is a collection of connected peninsulas and nearby islands. The two largest peninsulas are mainland Europe and Scandinavia to the north, divided from each other by the Baltic Sea. Three smaller peninsulas—Iberia, Italy and the Balkans—emerge from the southern margin of the mainland. The Balkan peninsula is separated from Asia by the Black and Aegean Seas. Italy is separated from the Balkans by the Adriatic Sea, and from Iberia by the Mediterranean Sea, which also separates Europe from Africa.
North Sea sea grass used to coat huge tracts of ocean floor, but have been damaged by trawling and dredging have diminished its habitat and prevented its return. Invasive Japanese seaweed has spread along the shores of the sea clogging harbours and inlets and has become a nuisance. Due to the heavy human populations and high level of industrialization along its shores, the wildlife of the North Sea has suffered from pollution, overhunting, and overfishing. Flamingos and pelicans were once found along the southern shores of the North Sea, but became extinct over the 2nd millennium. Walruses frequented the Orkney Islands through