The Adaja is a river of Spain located in the centre of the Iberian Peninsula, a major left-bank tributary of the Douro.

[1] Featuring a total length of 163 km, its river basin drains an area of 5,328 km2.

[2] It has its source in the so-called Fuente Berroqueña (Villatoro, province of Ávila), near the saddle point between La Serrota [es] and the Sierra de Ávila.

[2] Initially following a Southwest-Northeast course through the Amblés Valley, the Adaja bends towards the North in Ávila.

It receives the contribution of its most important tributary, the Eresma, near Matapozuelos,[3] emptying in the Douro in the province of Valladolid near the town of Aniago.