The Great Rift Valley runs through the country from north to south, and to the east of the valley lies Lake Malawi (also called Lake Nyasa), making up over three-quarters of Malawi's eastern boundary. Lake Malawi is sometimes called the Calendar Lake as it is about long and wide. The Shire River flows from the south end of the lake and joins the Zambezi River farther south in Mozambique. The surface of Lake Malawi is at above sea level, with a maximum depth of , which means the lake bottom is over below sea level at some points.