The Baltic Sea (The Baltic) is an arm of the Atlantic Ocean which opens into the North Sea by narrow channels between Denmark and Sweden. The Baltic Sea is nearly 1440 km long extending to 320 km broad. A chain of islands separates the southern part from the northern, or Gulf of Bothnia. In the north-east the Gulf of Finland stretches far into Russia, and separates Finland from Esthonia. The water of the Baltic is colder and clearer than that of the ocean, andf contains less salt. Research Baltic Sea