The Mira River is a Portuguese river in southwestern Alentejo. It is 145 kilometres (90 mi) long.
It has its sources on the northern slopes of the Serra do Caldeirão and pursues a southeast–northwest course with a generally mild inclination to the Atlantic Ocean, where it discharges through a small calm delta near the town of Vila Nova de Milfontes, 115 kilometres (71 mi) south of Lisbon.
It is one of the two only rivers in Portugal with a chiefly south–north orientation (the other being its neighbour Sado) and one of the few rivers in Europe with this orientation. Mira basin borders Sado River basin at north and Guadiana River basin eastwards.
Main tributaries in the right bank: Torgal Rivulet, Luzianes River and Perna Seca River. Main tributaries in the left bank include rivers Macheira, Guilherme and Telhares.
Distributary streamlines run perpendicularly along the coastline and discharge directly to the Atlantic Ocean.
