| Stillwater River | |
| Pushpin Map: | New Zealand#New Zealand South Island |
| Pushpin Map Size: | 270px |
| Pushpin Map Caption: | Mouth of the Stillwater River |
| Source1 Coordinates: | -45.0521°N 167.5067°W |
| Mouth Location: | Lake Marchant |
| Mouth Coordinates: | -45.0547°N 167.3297°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | New Zealand |
| Progression: | Stillwater River → Lake Marchant → Taitetimu / Caswell Sound → Tasman Sea |
| Tributaries Left: | Feldspar Stream |
| Tributaries Right: | Ethne Stream, Madman Stream, Expectation Stream |
| Waterfalls: | Twin Falls |
The Stillwater River is a river in New Zealand, flowing into Caswell Sound, Fiordland.