The Sea of Azov is an extension of the Black Sea situated off the southern shores of Russia and Ukraine. It covers an area of 15,000 square miles and its waters, averaging a depth of seven metres, are the shallowest in the world. In ancient times it was known as Lake Maeotis. Although it teems with aquatic life, the Sea freezes over entirely between November and March, and in warmer seasons much of it is reduced to swamp and quagmire. Its westernmost reach, now called Sivash, was referred to as the Putrid Lake by the Ancient Greeks.