Tallinn is situated on the southern coast of the Gulf of Finland, in north-western Estonia. The largest lake in Tallinn is Lake Ülemiste (9.44 km2 (3.6 sq mi)). It is the main source of the city's drinking water. Lake Harku is the second largest lake within the borders of Tallinn and its area is 1.6 square kilometres (0.6 sq mi). Tallinn does not lie on a major river. The only significant river in Tallinn is Pirita River in Pirita, a city district counted as a suburb. Historically, the small Härjapea River flowed from Lake Ülemiste through the town into the sea, but the river was diverted for sewage in the 1930s and has since completely disappeared from the cityscape. References to it still remain in the street names Jõe (from Jõgi, river) and Kivisilla (from Kivisild, stone bridge). A limestone cliff runs through the city. It can be seen at Toompea, Lasnamäe and Astangu. However, Toompea is not a part of the cliff, but a separate hill. The highest point in Tallinn, at 64 meters above sea level, is situated in Hiiu, Nõmme District, in the south-west of the city. The length of the coast is 46 kilometres (29 miles). It comprises three bigger peninsulas: Kopli peninsula, Paljassaare peninsula and Kakumäe peninsula.