The Guadiela is a river in the Iberian Peninsula, a left-bank tributary of the Tagus and the latter's major upper-course tributary.

[1][2] The Guadiela has its source in the Serranía de Cuenca [es], near Cueva del Hierro,[3] at the Fuente Pinilla site.

[4] It flows from East to West for 117 kilometres (73 mi),[2] passing through the Spanish province of Cuenca, emptying into the Tagus at the Bolarque reservoir,[5] on the border between the provinces of Cuenca and Guadalajara.

It is dammed upstream by the Buendía reservoir [es].

[2] The hydronym Guadiela is formed by 'Guad' (of Arabic origin, conveying the meaning of "river") and the '-iela' suffix (a diminutive).