The country is a broad tableland with a mean altitude of 1,000 m (3,300 ft). A vast plateau about 1,200 m (4,000 ft) in height, extending from near Kanye north to the Zimbabwean border, divides the country into two distinct topographical regions. The eastern region is hilly bush country and grassland (veld). To the west lie the Okavango Swamps and the Kalahari Desert. The only sources of year-round surface water are the Chobe River in the north, the Limpopo in the southeast, and the Okavango in the northwest. In seasons of heavy rainfall, floodwaters flow into the Makgadikgadi Salt Pans, Lake Ngami, and Lake Xau.