The Senegal's headwaters are the Semefé (Bakoye) and Bafing rivers which both originate in Guinea; they form a small part of the Guinean-Malian border before coming together at Bafoulabé in Mali. From there, the Senegal river flows west and then north through Talari Gorges near Galougo and over the Gouina Falls, then flows more gently past Kayes, where it receives the Kolimbiné. After flowing together with the Karakoro, it prolongs the former's course along the Mali-Mauritanian border for some tens of kilometers till Bakel where it flows together with the Falémé River, which also has its source in Guinea, subsequently runs along a small part of the Guinea-Mali frontier to then trace most of the Senegal-Mali border up to Bakel. The Senegal further flows through semi-arid land in the north of Senegal, forming the border with Mauritania and into the Atlantic. In Kaedi it accepts the Gorgol from Mauritania. Flowing through Bogué it reaches Richard Toll where it is joined by the Ferlo coming from inland Senegal's Lac de Guiers. It passes through Rosso and, approaching its mouth, around the Senegalese island on which the city of Saint-Louis is located, to then turn south. It is separated from the Atlantic Ocean by a thin strip of sand called the Langue de Barbarie before it pours into the ocean itself.
The river has two large dams along its course, the multi-purpose Manantali Dam in Mali and the Maka-Diama Dam downstream on the Mauritania-Senegal border, near the outlet to the sea, preventing access of salt water upstream. In between Manantali and Maka-Diama is the Félou Hydroelectric Plant which was originally completed in 1927 and uses a weir. The power station was replaced in 2014. In 2013, construction of the Gouina Hydroelectric Plant upstream of Felou at Gouina Falls began.
Downstream of Kaédi the river divides into two branches. The left branch called the Doué runs parallel to the main river to the north. After 200 km the two branches rejoin a few kilometres downstream of Pondor. The long strip of land between the two branches is called the Île á Morfil.
In 1972 Mali, Mauritania and Senegal founded the Organisation pour la mise en valeur du fleuve Sénégal (OMVS) to manage the river basin. Guinea joined in 2005.