| Rien | |
| Pushpin Map: | Trøndelag#Norway |
| Pushpin Label Position: | bottom |
| Pushpin Map Caption: | Location of the lake |
| Coordinates: | 62.7402°N 11.8845°W |
| Location: | Røros, Trøndelag |
| Outflow: | Glomma |
| Catchment: | Glommadal |
| Basin Countries: | Norway |
| Area: | 14.87km2 |
| Reference: | NVE |
Rien is a lake in the municipality of Røros in Trøndelag county, Norway. The 14.87km2 lake is located near the headwaters of the river Glomma, only about west of the border with Sweden. The water flows out through the river Glomma and heads a short distance south, into the large lake Aursunden. The village of Brekken lies about south of the lake and the town of Røros lies about to the southwest.