Encompassing most of a rocky island 500 feet from the mainland in Rockport, the wildlife sanctuary is adjacent to the town-owned historic lighthouse and lies within a designated Important Bird Area (IBA).

The island is covered with dense vegetation of shrubs, brambles, and poison ivy, which makes access to and across the island difficult. Mass Audubon worked with the Town of Rockport and the Thacher Island Association to restore and maintain the lighthouse and lighthouse keeper residence, which are both historically significant structures. As of 2020, the island has a composting toilet at the landing.

Please be sure to sign in at the Keeper House with the Thacher Island Association volunteer keepers. The island is open from May 15 to August 30, or whenever the Lighthouse Keepers are in attendance.

Straitsmouth Island is off the coast of Rockport and is accessible by kayak.

Explore the 0.33-mile trail through the center of the island that passes several historic points of interest along the way.