The Draa (Arabic: وادي درعة, romanized: wādī dar'a; also spelled Dra or Drâa, in older sources mostly Darha or Dara) is Morocco's longest river, at 1,100 kilometres (680 mi). It is formed by the confluence of the Dadès River and Imini River. It flows from the High Atlas mountains, initially south-eastward to Tagounite, and from Tagounite mostly westwards to its mouth in the Atlantic Ocean somewhat north of Tan-Tan. In 1971, the (El) Mansour Eddahabi dam was constructed to service the regional capital of Ouarzazate and to regulate the flow of the Draa. Most of the year the part of the Draa after Tagounite falls dry. In the first half of the 20th century, the lowest course of the Draa marked the boundary between the French protectorate of Morocco and the area under Spanish rule. The valley contains the Fezouata formations, which are Burgess shale-type deposits dating to the Lower Ordovician, filling an important preservational window between the common Cambrian lagerstätten and the Late Ordovician Soom shale. In the fossilized fauna were numerous organisms previously thought to have died out after the mid-Cambrian.
