| Hammergraben | |
| Mouth Location: | Großes Fließ |
| Mouth Coordinates: | 51.8544°N 14.2608°W |
| Progression: | Großes Fließ→ |
| Subdivision Type1: | Country |
| Subdivision Name1: | Germany |
| Subdivision Type2: | States |
| Subdivision Name2: | Brandenburg |
Hammergraben is a river of Brandenburg, Germany. It branches off the Spree in Cottbus, and flows into the Großes Fließ (a tributary of the Spree) in Schmogrow-Fehrow. It is used to flood Cottbuser Ostsee, a former open pit lignite mine, which is planned to become Germany's largest artificial lake by surface area.