| Guadalix | |
| Subdivision Type1: | Country |
| Subdivision Name1: | Spain |
| Length: | 42km (26miles) |
| Source1 Location: | Miraflores de la Sierra |
| Source1 Coordinates: | 41.0153°N -3.8511°W |
| Mouth: | Jarama |
| Mouth Location: | Algete |
| Mouth Coordinates: | 40.6161°N -3.5733°W |
The Guadalix is a river of Spain located in the centre of the Iberian Peninsula, a right-bank tributary of the Jarama.
It springs out of the Sierra de Guadarrama, in the valley flanked by the, el, the Alto de la Genciana and the Cordal de la Vaqueriza.[1] Featuring a total length of 42 km,[2] it runs southeastwards through the Community of Madrid until discharging in the Jarama near the Santo Domingo housing development (Algete),[3] next to the Jarama Circuit.
Its waters are impounded by the .
Regarding the etymology of the hidronym Guadalix; the prefix comes from the Arabic wadi ("river") while the suffix -alix has been identified either as an alleged Arab anthroponym or as possibly pre-Arab.[4]