The central and northern parts of the country lie within the North European Plain. Rising above these lowlands is a geographical region comprising four hilly districts of moraines and moraine-dammed lakes formed during and after the Pleistocene ice age, notably the Pomeranian Lake District, the Greater Polish Lake District, the Kashubian Lake District, and the Masurian Lake District. The Masurian Lake District is the largest of the four and covers much of north-eastern Poland. The lake districts form a series of moraine belts along the southern shore of the Baltic Sea.