| Waihopai River | |
| Subdivision Type1: | Country |
| Subdivision Name1: | New Zealand |
| Subdivision Type2: | Region |
| Subdivision Name2: | Marlborough |
| Source1: | Waihopai Saddle |
| Source1 Coordinates: | -41.9069°N 173.2131°W |
| Mouth: | Wairau River |
| Mouth Coordinates: | -41.5108°N 173.7261°W |
| River System: | Wairau River |
| Tributaries Right: | Spray River, Avon River |
The Waihopai River—the more northerly of two New Zealand rivers of that name—runs through the South Island's Marlborough Region and is a major tributary of the Wairau River. The river has its source in the Raglan Range of mountains, some 70km (40miles) northwest of Kaikōura. It runs in a generally northeastward direction for all of its length, the first section of which is through narrow alpine valleys. After joining its major tributary, the Spray River, the valley begins to widen, becoming a broad valley by the time the second main tributary, the Avon River is reached. For the last 15km (09miles) of its length the Waihopai turns northward, reaching the Wairau 7km (04miles) west of Renwick.