| Blackwater River | |
| Map: | Blackwater River (River Axe) map.png |
| Subdivision Type1: | Country |
| Subdivision Name1: | England |
| Subdivision Type2: | Counties |
| Subdivision Name2: | Devon, Dorset |
| Length: | 10km (10miles) |
| Source1 Location: | Marshwood, Dorset |
| Source1 Coordinates: | 50.7995°N -2.875°W |
| Mouth: | River Axe |
| Mouth Coordinates: | 50.8164°N -2.9599°W |
The Blackwater River is a 10km (10miles) long river in the counties of Dorset and Devon, in the south-west of England. It rises to the north of Marshwood in Dorset, flowing north and west to join the River Axe at a point north of Axminster in Devon. For most of its length it forms the county boundary between Dorset and Devon.[1] [2]