Tewksbury Rock is a small subsurface rock pinnacle located in Massachusetts Bay

Massachusetts Bay

The Massachusetts Bay, also called Mass Bay, is one of the largest bays of the Atlantic Ocean which forms the distinctive shape of the coastline of the U.S. state of Massachusetts. Its waters extend 65 miles into the Atlantic Ocean. Massachusetts Bay includes the Boston Harbor, Dorchester Bay,...

, within the city limits of Boston. The rock is northeast of Outer Brewster Island, west of Martin Ledge

Martin Ledge (Massachusetts)

Martin Ledge is small barren rocks that barely stick out of the waters of Massachusetts Bay, within the city limits of Boston, Massachusetts, USA. The rocks are east of Tewksbury Rock and Outer Brewster Island and southwest of Three and One-half Fathom Ledge....

, and far north of Boston Ledge

Boston Ledge (Massachusetts)

Boston Ledge is a small barren rock in Massachusetts Bay, within the city limits of Boston. The rock is far south of Tewksbury Rock and far northeast of Shag Rocks....

. It is 15 feet (4.6 m) to 18 feet (5.5 m) below the surface of the water, but more than 45 feet (13.7 m) above the hard gravel floor of the bay.