The Senegal River runs along Mauritania's southern border with Senegal. It's Mauritania's only major river and the only one in the country that flows year-round. Because of this, it is a critical water source for the largely arid Mauritania and has been the source of numerous deadly conflicts between Mauritania and Senegal. Land around the Senegal in southern Mauritania is green fields, home to numerous species of birds and small mammals, in contrast to the Saharan sands that cover much of the rest of the country. The Mauritania-Senegal border makes up about half of the Senegal River's total 1,020-mile stretch.
The Gorgol River is a small tributary of the Senegal River, branching off near the southern Mauritania town of Kaedi and flowing through the Gorgol Valley. Like the Senegal, the Gorgol is a critical source of irrigation for farming in the area. Although the area around the Gorgol itself is densely populated, it is remote within Mauritania and thus has virtually no modern infrastructure, according to Rainbow Development. The area also is susceptible to both severe droughts and devastating floods.
The Karakoro River is another tributary of the Senegal, flowing south from the area around the city of Kiffa. It forms part of Mauritania's border with Mali. For most of its length, the Karakoro is only a few yards wide, but it swells to more than 800 feet wide for about a 7.5-mile stretch near the town of Kankossa. Despite this proximity, water shortages remain a persistent problem for Kankossa, particularly during the dry season. South of Kankossa, the Karakoro has another shorter but wider stretch before it meets the Senegal.
The Kolimbine River continues Mauritania's border with Mali, to the northeast of where the Karakoro River flows. It begins in southern Mauritania and flows south, eventually emptying into the Senegal River near Kayes, a city in western Mali. For about a 38-mile stretch, the Kolimbine crosses several lakes. Between those lakes, the Kolimbine is intermittent and is a dry riverbed in several spots.