| Trettach | |
| Mouth Coordinates: | 47.4273°N 10.274°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | Germany |
| Subdivision Type2: | State |
| Length: | 15.6km (09.7miles) |
| Basin Size: | 157km2 |
Trettach is a river of Bavaria, Germany. At its confluence with the Breitach and the Stillach in Oberstdorf, the Iller is formed.