Ponkapag Pond is a 203-acre impoundment in the Blue Hills Reservation. The pond is located on the border of Canton and Randolph, Massachusetts about a half mile south of Route 128 and a half mile east of Route 138. It has a maximum depth of seven feet and an average depth of four feet. As would be expected on a pond this shallow, aquatic vegetation is pervasive and very abundant. Only a small portion of the eastern shoreline is developed; the southeastern and western shores are bordered by large expanses of marshland. A walking trail circles the pond, with parking at three locations.