Its watershed covers 392.57 acres (158.87 ha); 52.08 acres (21.08 ha) is occupied by water. Maschaug itself has a surface area of 34.63 acres (14.01 ha), while nearby Little Maschaug Pond is 11.69 acres (4.73 ha). The pond averages 6.89 ft (2.10 m) deep, and has a salinity level of approximately 7 parts per thousand, too low to sustain the growth of eelgrass.[2][5] The pond is non-tidal, except when breached by storms.[5] The water directly receives about 57,219,222 gallons of precipitation per year, though groundwater flow is unknown. No rivers or streams flow into the pond.[6] Maschaug Pond, like others in the region, was "formed after the recession of the glaciers 12,000 years ago".[7]
As a result of certain environmental conditions, including low elevation of surrounding land and dense residential and commercial development, Maschaug Pond is considered particularly susceptible to storm surge. It is projected that during a future hurricane, Winnapaug and Maschaug Ponds will likely be significantly changed.[4]