Massachusetts Bay and Boston Harbor

sandy and pebbly beach with a stormy sky above
A stormy sky over Nantasket Beach on the outer harbor. A sandy beach with small dark shells runs up along the right side of the frame. Two people stand in the distance. The water and horizon occupies the left frame. Above the horizon is a dark grey cloudy sky with patches of white clouds.

NPS Photo/Lampley

The Massachusetts Bay extends for over forty miles from Cape Ann in the north to Plymouth Harbor in the south on the eastern coast of the Commonwealth. It is a major feature of the North Atlantic Ocean and is part of the greater Gulf of Maine ecosystem. The most prominent submerged feature within the Massachusetts Bay is the Stellwagen Bank on its eastern edge, which is a shallow, mostly sandy plateau that curves from northwest to southeast for about nineteen miles. Established in 1992, the Stellwagen Bank National Marine Sanctuary conserves submerged shipwrecks and protects populations of whales and commercial fish.

navigational chart of boston harbor
The navigational map shows the coastline of Greater Boston with additional details of roads  and elevation along the shoreline. Land is marked in a pale tan color, with a deeper tan surrounding the coasts. Harbor Islands are marked in a grey-blue color.

U.S. Coast Survey, 1878 (Boston Public Library)

Within the Massachusetts Bay is the Boston Bay. And within the Boston Bay, enclosed by Deer Island to the north and the wide arm of Hull to the south, is the interior of Boston Harbor, a famously complicated navigational harbor with shallow channels, many of the Boston Harbor Islands, submerged bars, and—in places—strong currents. The entire harbor is relatively shallow, on average less than twenty feet deep, and so to maintain its commercial viability it is routinely dredged in key areas to maintain suitable depth for large craft. The main channel that runs through President Roads between Deer Island and Gallops Island, then into the Inner Harbor and Mystic River Basin industrial port is maintained by dredging to support container ships. The Boston Harbor Deep Draft Navigation Project is dredging the channel to 47 feet depth.

view of the harbor through some tall grass spikes
Late summer grass spikes at Deer Island. Tall thin stalks rise in the foreground, capped with thin brown spikes that nod down to the right in the wind. Behind the grass is a low granite wall before a dark blue sea extending to the horizon. The sky is clear and blue, with two big fluffy clouds.

NPS Photo/Lampley

For much of the past four centuries the harbor has been indiscriminately used as a dumping spot for detritus and human waste, leading to its reputation in the 1980’s as the “harbor of shame.” The Harbor Islands were used as landfills, horse-rendering plants, quarantine hospitals, prisons, internment camps, and other activities unwanted on the mainland. That all changed in the 1980s with a court – ordered cleanup and the establishment of the Massachusetts Water Resources Authority, which oversaw the Boston Harbor Cleanup and the construction and operation of the Deer Island Wastewater Treatment Plant, which maintains clean harbor waters today. Since the cleanup, Boston’s downtown “central artery” highway was moved to an underground tunnel and the Rose Kennedy Greenway was created along the downtown waterfront, and redevelopment has placed recreational and scenic values of the harbor as a centerpiece. The cleanup has also led to significant improvements in water quality and marine ecosystems and species. Heavy metals and other long-lasting, heavy pollutants remain in the harbor floor sediments, however, and shellfishing and groundfishing remains closed due to public health concerns.

Last updated: November 3, 2021

Park footer

Contact Info

Mailing Address:

Boston Harbor Islands National and State Park
21 Second Ave

Charlestown, MA 02129


617 223-8666

Contact Us