The Upper Salmon River divides Fundy National Park and the village of Alma, New Brunswick at its delta. Here, it is inundated with tidal water from the Salisbury Bay (Chignecto Bay) a kilometer to the site of a former dam, making for a large estuary and inter-tidal zone. Its watershed catchment drains a large area in and outside the park, made up of tributaries and their sub-units including Kinnie Brook, Laverty, Forty-five River, Lake Brook, Greenough Brook, and others.
It is a sub-unit within the Chignecto Bay North Watershed, an area designated under the UNESCO Programme on Man and the Biosphere. Macro-regionally, it is part of the Gulf of Maine watershed.