| Arga | |
| Name Other: | (Runa) |
| Subdivision Type1: | Country |
| Subdivision Name1: | Spain |
| Subdivision Type3: | Region |
| Subdivision Name3: | Navarre |
| Subdivision Type5: | City |
| Subdivision Name5: | Pamplona |
| Length: | 145km (90miles) |
| Discharge1 Avg: | 59.76m3/s |
| Source1 Location: | near Esteríbar |
| Mouth Location: | Aragón River |
| Mouth Coordinates: | 42.2967°N -1.7853°W |
The Arga is a river of Navarre, in Spain, and is a tributary of the Aragón River, itself a tributary of the river Ebro. The Arga was known as the river Runa in antiquity. Situated in the north-east of Spain, the river stretches some 145km (90miles) and has a basin of 2759km2, of which 2652km2 is in Navarre and the remaining 107km2 is in the province of Alava. The source of the river is to the north of the village Esteríbar, near the border with France, and it empties into the Aragón River near Funes.
The river is dammed in the Eugui reservoir near Esteríbar; the dam principally serves the needs of Pamplona's metropolitan area, the largest city on the Arga.
At the upper basin, the river is mainly surrounded by beech trees and beneath these grow bilberries, Cornish heath, sedges and luzulas. Additionally, a variety of shrubs can be found in the proximity of the Eugui reservoir, including; alder, ash, maple, common hazel and buckthorn. After the dam, the lower river is lined with oak and Scots pine trees and boxwood shrubs.
At the point where the river passes Huarte/Uharte, a crack willow appears. The shrubbery around the area of Belascoáin marks the change from Cantabrian forest to more Mediterranean plant life; black poplar and white willow are common in this region.