| Marycha | |
| Mouth Location: | Czarna Hańcza |
| Mouth Coordinates: | 53.903°N 23.648°W |
| Progression: | Czarna Hańcza→ |
| Subdivision Type1: | Country |
| Subdivision Name1: | Poland, Lithuania, Belarus |
| Length: | 80.8km (50.2miles) |
| Basin Size: | 432.4km2 |
Marycha (Lithuanian: Seina) is a small river that serves as the natural Polish–Lithuanian and Lithuanian–Belarusian border. It starts around Puńsk, flows through the town of Sejny, passes through Pomorze Lake. It is a tributary of Czarna Hańcza.