Wales is about 8,000 square miles in area, which is about the size of the state of Massachusetts. Wales is a land of wild and rugged beauty. Its coastline is deeply indented with bays and off the northwest coast is the island of Anglesey, which forms a county of Wales. Most of the region consists of highlands, with mountains rising in the northwest and southeast. There is a coastal plain around three sides. Most of the people live on the coastal plain. The principal river of Wales is the Severn. Others are the Taff, the Usk, the Wye, and the Dee. There are two important lakes: Lake Bala in the north, which is the source of the Dee; and Lake Vyrnwy. In the western part of Wales the climate is cool in summer and mild in winter; in the eastern part the summers are warm and the winters cold. Rainfall is heavy throughout the region.