| Forthbach | |
| Mouth Location: | Grubebach |
| Mouth Coordinates: | 51.8148°N 8.3638°W |
| Progression: | Grubebach→ |
| Subdivision Type1: | Country |
| Subdivision Type2: | State |
| Length Km: | 19.5 |
Forthbach is a river of North Rhine-Westphalia, Germany. It flows into the Grubebach near Rheda-Wiedenbrück.