Aaron River Reservoir is a 136-acre (0.55 km²) reservoir mostly in Cohasset, Massachusetts, with small stretches extending into Hingham and Scituate. The outflow of the pond is Aaron River. Most of the reservoir is in the eastern side of Wompatuck State Park. The village of Beechwood lies to the east of the reservoir. The reservoir is a Class A water supply source used as a backup source for the Town of Cohasset.