| Blackwater River | |
| Pushpin Map: | New Hampshire#Massachusetts#USA |
| Pushpin Map Size: | 250 px |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | States |
| Subdivision Name2: | Massachusetts, New Hampshire |
| Subdivision Type3: | Counties |
| Subdivision Name3: | Essex County, MA |
| Subdivision Type4: | Towns |
| Subdivision Name4: | Salisbury, MA |
| Length: | 3.1miles |
| Source1 Location: | Salisbury, MA |
| Source1 Coordinates: | 42.8667°N -70.8228°W |
| Source1 Elevation: | 0feet |
| Mouth: | Hampton Harbor |
| Mouth Location: | Seabrook, NH |
| Mouth Coordinates: | 42.8889°N -70.8272°W |
| Mouth Elevation: | 0feet |
The Blackwater River is a 3.1adj=midNaNadj=mid tidal inlet in northeastern Massachusetts and southeastern New Hampshire in the United States.[1]
The river forms in a salt marsh in the northeastern corner of Salisbury, Massachusetts, by the convergence of the Little River and Dead Creek. Heading north, the river quickly enters Seabrook, New Hampshire and continues to flow through salt marsh until it reaches Hampton Harbor, northwest of Seabrook Beach, where it joins the Hampton River.