The name also refers to the geographic region around the two countries, covering the watershed of the Senegal River and Gambia River. For the term related to television programmes, see watershed (television). ... The Senegal River, in West Africa, forms the border between Senegal and Mauritania. ... Gambia River from space The Gambia River is a major river in Africa, running 1,130 km (700 miles) from the Fouta Djallon plateau in north Guinea to the Atlantic Ocean at the city of Banjul. ...