Middle Brewster Island is a rugged outer island in the Boston Harbor Islands National Recreation Area, located 9 miles (14 km) offshore from downtown Boston. The island has a permanent size of 13 acres (53,000 m²), reaches a height of 52 feet (16 m) above sea level, and is bounded by sharp cliffs and sunken crags. It has only sparse vegetation and serves primarily as a nesting site for gulls and cormorants. The birds are aggressive during their nesting season and access by humans is discouraged during this period.