Moon Island (Massachusetts)

Moon Island is one of the Boston Harbor Islands, located in Quincy, Massachusetts. It is part of the Boston Harbor Islands National and State Park. The island is connected to the mainland via a two-lane causeway, making it technically a tied island.

Historically, Moon Island has served several purposes, primarily related to public health and safety. In the 19th century, it housed a quarantine hospital and an almshouse, aimed at isolating and treating individuals with contagious diseases and providing care for the poor.

Perhaps most notably, Moon Island is the site of the Deer Island Sewage Treatment Plant's effluent outfall. Partially treated sewage from the Greater Boston area is discharged into Massachusetts Bay through a deep-rock tunnel that terminates several miles offshore from Moon Island. The presence of this outfall has made the island largely inaccessible to the public for decades, primarily due to security concerns surrounding the infrastructure.

While technically part of the Boston Harbor Islands National and State Park, public access to Moon Island is restricted due to its critical role in the region's wastewater management system. Occasional guided tours and educational programs may be offered, but unauthorized entry is prohibited. The island's use as a wastewater facility significantly limits its recreational or natural resource potential within the park system.