The Gambia River, the country's major waterway, rises in Guinea and follows a twisting path for about 1,600 km (1,000 mi) to the sea. In its last 470 km (292 mi), the river flows through the Republic of The Gambia, narrowing to a width of 5 km (3 mi) at Banjul; during the dry season, tidal saltwater intrudes as far as 250 km (155 mi) upstream. Brown mangrove swamps line both sides of the river for the first 145 km (90 mi) from the sea; the mangroves then give way to more open country and, in places, to red ironstone cliffs. The land on either side of the river is generally open savanna with wooded areas along the drainage channels. Elevation reaches a maximum of 73 m (240 ft).