| Salmon Brook | |
|---|---|
| Origin | Martins Pond |
| Mouth | Merrimack River |
| Basin countries | USA |
| Length | 17.5 miles (28.2 km) |
| Source elevation | 280 feet (85 m) at Groton, Massachusetts |
| Avg. discharge | 150 ft³/s |
| Basin area | 36 square miles (93 km2) |
Salmon Brook is one of the 6 major tributaries of the Merrimack River in northeastern Massachusetts in the United States. Its watershed is 31 square miles (80 km2) and is one of the 14 subwatersheds of the Merrimack River. It passes through Groton, Dunstable, and Tyngsborough, Massachusetts, and then through Nashua, New Hampshire.
Salmon Brook begins at Martins Pond in Groton. It then flows approximately 17.5 miles (28.2 km) north-northeast to the Merrimack River. It runs through Lost Lake (Groton)/ Knopps Pond, Whitney Pond, and Massapoag Ponds. All of these water bodies are dammed. The brook runs roughly parallel to the Nashua River from Lost Lake to the brook's mouth in Nashua.