What river originates 150 miles from the ocean then flows for 2,600 miles before entering the ocean?

The Niger takes one of the most unusual routes of any major river, a boomerang shape that baffled geographers for two centuries. Its source (Tembakounda) is just 240 km (150 mi) inland from the Atlantic Ocean, but the river runs directly away from the sea into the Sahara Desert, then takes a sharp right turn near the ancient city of Timbuktu (Tombouctou) and heads southeast to the Gulf of Guinea.

This strange geography apparently came about because the Niger River is two ancient rivers joined together. The upper Niger, from the source west of Timbuktu to the bend in the current river near Timbuktu, once emptied into a now dry lake to the east northeast of Timbuktu, while the lower 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.[10]

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 desert. This made it the focal point of trade across the western Sahara, and the centre of the Sahelian kingdoms of Mali and Gao.