Valday Hills or Valdai Hills, upland region, NW European Russia, composed of a series of glacial moraines that rise to c.1,100 ft (340 m). The region forms the watershed of the upper Volga, the Western Dvina, and the Dnieper rivers and also of the rivers that flow into Lake Ilmen. Numerous glacial lakes are found there. Among them, Lake Seliger is the largest.