Lake Vostok is the largest of more than 140 subglacial lakes found under the surface of Earth's southern-most continent -- Antarctica. It is located at 77° S 105° E, beneath Russia's Vostok Station, 4,000 meters (13,000 feet) under the surface of the central Antarctic ice sheet. It is 250 km long by 50 km wide at its widest point, thus similar in size to Lake Ontario, and is divided into two deep basins by a ridge. The water over the ridge is about 200 m (650 feet) deep, compared to roughly 400 m (1,300 feet) deep in the northern basin and 800 m (2,600 feet) deep in the southern. Lake Vostok covers an area of 15,690 km² (6,058 mi²). It has an estimated volume of 5,400 km³ (1,300 cubic miles) and consists of fresh water. The average depth is 344 m. In May 2005 an island was found in the center of the lake.