Deer Island is a small island located in Boston Harbor, Massachusetts. It covers approximately 1,200 acres and is primarily known for its role in wastewater treatment. The island is home to the Deer Island Wastewater Treatment Plant, which processes sewage for the Greater Boston area, helping to protect the local environment. In addition to its industrial use, Deer Island features walking trails and scenic views of the harbor. The island is accessible by ferry and offers recreational opportunities for visitors, including birdwatching and fishing. It is also part of the Boston Harbor Islands National and State Park, which includes several other islands in the area.