The Powwow River is a 22.8-mile-long river located in New Hampshire and Massachusetts. It is a tributary of the Merrimack River, part of the Gulf of Maine watershed.

The Powwow River rises in the center of Danville and flows southeasterly through Long Pond into Kingston, where it enters Great Pond, a 268-acre water body in the center of the town. Leaving Great Pond, the river enters an extensive network of wetlands and receives a major tributary from the southwest, the outlet of Country Pond, situated in Kingston and Newton. Continuing east, the Powwow River enters Powwow Pond and passes into the southwest corner of East Kingston, flowing over Trickling Falls Dam at NH-107. The river turns southeast and enters South Hampton, where it flows into Tuxbury Pond and crosses into Amesbury, Massachusetts. Below the outlet of the pond, the river winds easterly along the state line before entering Massachusetts for good at Lake Gardner. The river then flows through the center of Amesbury, where it drops over falls and rapids before reaching the Merrimack River.