Title: Niger River
Content:  Niger started to the south of Timbuktu and flowed south into the Gulf of Guinea. Over time upstream erosion by the lower Niger resulted in stream capture of the upper Niger by the lower Niger. The northern part of the river, known as the Niger bend, is an important area because it is the major river and source of water in that part of the Sahara. This made it the focal point of trade across the western Sahara and the centre of the Sahelian kingdoms of Mali and Gao. The surrounding Niger River Basin is one of the distinct physiographic sections of the Sudan province, which in turn is part of the larger African massive physiographic division.
Title: Niger River
Content:   The Niger River ((le) fleuve Niger, ) is the main river of West Africa, extending about 4180 km. Its drainage basin is 2117700 km2 in area. Its source is in the Guinea Highlands in southeastern Guinea near the Sierra Leone border. It runs in a crescent through Mali, Niger, on the border with Benin and then through Nigeria, discharging through a massive delta, known as the Niger Delta (or the Oil Rivers), into the Gulf of Guinea in the Atlantic Ocean. The Niger is the third-longest river in Africa, exceeded only by the Nile and the Congo River (also known as the Zaïre River). Its main tributary is the Benue River.
Title: Niger
Content:  Niger or the Niger ( or ;  ), officially the Republic of the Niger,  (Jamhuriyar Nijar, Zarma-Songhai: Nigér Laabo, جمهورية النيجر) is a landlocked country in West Africa named after the Niger River. Niger is a unitary state bordered by Libya to the northeast, Chad to the east, Nigeria to the south, Benin and Burkina Faso to the southwest, Mali to the west, and Algeria to the northwest. Niger covers a land area of almost 1,270,000 km2, making it the second-largest landlocked country in West Africa (behind Chad). Over 80% of its land area lies in the Sahara Desert. The country's predominantly Muslim population of about million live mostly in clusters in 
Title: Lazaret, Niger
Content:  The Sahel is a belt of grassland and savanna, with areas of woods and shrubs, that runs along the southern rim of the Sahara desert. It includes parts of Senegal, Mauritania, Mali, Burkina Faso, Niger, and Chad. The people of the region mostly live through herding, farming and fishing. Farming in most areas depends on the rain that falls during a three-month period of the summer, although irrigation is practiced along the banks of rivers and lakes. The region is subject to periodic droughts.
Title: Niger
Content:   Niger is a landlocked nation in West Africa located along the border between the Sahara and Sub-Saharan regions. It borders Nigeria and Benin to the south, Burkina Faso and Mali to the west, Algeria and Libya to the north and Chad to the east. Niger lies between latitudes 11° and 24°N, and longitudes 0° and 16°E. Niger's area is 1267000 km2 of which 300 km2 is water. This makes it slightly less than twice the size of France, and the world's twenty-second largest country. Niger borders seven countries and has a total perimeter of 5697 km. The longest border is with Nigeria to the south (1497 km). This is followed by Chad to the east, at 1175 km, Algeria to the north-northwest (956 km), and Mali at 821 km. Niger also has small borders in its far southwest with Burkina Faso at 628 km and Benin at 266 km and to the north-northeast Libya at 354 km. The lowest point is the Niger River, with an elevation of 200 m. The highest point is Mont Idoukal-n-Taghès in the Aïr Mountains at 2022 m.
Title: Niger River
Content:  the Sahel, was a key origin and destination for trans-Saharan trade, fueling the wealth of great empires such as the Ghana, Mali, and Songhai Empires. Major trading ports along the river, including Timbuktu and Gao, became centers of learning and culture. Trade to the Niger bend region also brought Islam to the region in approximately the 14th century CE. Much of the northern Niger basin remains Muslim today, although the southern reaches of the river tend to be Christian. Classical writings on the interior of the Sahara begins with Ptolemy, who mentions two rivers in the desert: the "Gir" (Γειρ) and farther south, the "Nigir" (Νιγειρ). The first has been since identified 
Title: List of tributaries of the Niger
Content: Sirba River 
Title: Sirba River
Content:  The Sirba River is a tributary of the Niger River in western Africa. The Sirba arises in Burkina Faso and flows east, crosses into Niger and then forms a short part of the international border between the two countries. It meets the Niger River at the midway point between the settlements of Gothèye and Karma in Niger, about 50 kilometres upstream from Niamey.
Title: Niger River
Content:   The Niger River is a relatively "clear" river, carrying only a tenth as much sediment as the Nile because the Niger's headwaters lie in ancient rocks that provide little silt. Like the Nile, the Niger floods yearly; this begins in September, peaks in November, and finishes by May. An unusual feature of the river is the Inner Niger Delta, which forms where its gradient suddenly decreases. The result is a region of braided streams, marshes, and large lakes; the seasonal floods make the Delta extremely productive for both fishing and agriculture. The river loses nearly two-thirds of its potential flow in the Inner Delta between Ségou and Timbuktu to seepage and evaporation. All the water from the Bani River, 
Title: Geography of Sudan
Content:  now, silt deposits have curtailed the overall flow. North of Khartoum, the Nile flows through the desert in a large S-shaped pattern to empty into Lake Nasser behind the Aswan High Dam in Egypt. The river flows slowly beyond Khartoum, dropping little in elevation, although five cataracts hinder river transport at times of low water. The Atbarah River, flowing out of Ethiopia, is the only tributary north of Khartoum, and its waters reach the Nile for only the six months between July and December. During the rest of the year, the Atbarah’s bed is dry, except for a few pools and ponds.

Question: through which countries of the sahel does the niger river flow?
Answer: Guinea.