| Williamson River | |
| Pushpin Map: | New Zealand#New Zealand South Island |
| Pushpin Map Size: | 270px |
| Pushpin Map Caption: | Mouth of the Williamson River |
| Subdivision Type1: | Country |
| Subdivision Name1: | New Zealand |
| Subdivision Type2: | region |
| Subdivision Name2: | West Coast Region |
| Subdivision Type3: | District |
| Subdivision Name3: | Westland District |
| Length: | 7.56km (04.7miles) |
| Source1: | Lake Williamson |
| Source1 Coordinates: | -44.4054°N 168.4069°W |
| Mouth: | Arawhata River |
| Mouth Coordinates: | -44.3863°N 168.4791°W |
| Progression: | Williamson River → Arawhata River → Jackson Bay / Okahu → Tasman Sea |
| River System: | Arawhata River basin |
| Tributaries Left: | Pass Creek, Tornado Creek, Topsey Creek |
The Williamson River is a minor river in the South Island of New Zealand.
It lies within the borders of the Mount Aspiring National Park and feeds into the Arawhata River.