| Ahja | |
| Pushpin Map: | Estonia |
| Pushpin Map Caption: | Location of mouth |
| Mouth: | Emajõgi |
| Subdivision Type1: | Country |
| Length: | 103.4km (64.2miles) |
| Source1 Elevation: | 87m (285feet) |
| Basin Size: | 1074.3km2 |
The Ahja (Estonian: Ahja jõgi) is a river in Estonia. The river is long. The river begins at Lake Erastvere and empties into the Emajõgi River. The river's middle course is protected by the Ahja River Valley Landscape Conservation Area.