Holly Marsh is a small saltwater marsh in Mashpee, Massachusetts, on Cape Cod beside Popponesset Bay. Beginning at Daniel's Island, a peninsula, it stretches along both the mainland shore and the Popponesset Island side of Popponesset Creek. As a coastal marsh connected to the creek and bay, it forms part of the low-lying shoreline around Popponesset. Its character comes from the meeting of tidal water, marsh edges, and the creek's narrow channel.