Hyannis Harbor lies midway along the south shore of Cape Cod in Hyannis, about 21 miles east of the harbor at Woods Hole and 16 miles west of Chatham. It consists of an outer harbor, a middle harbor (known as Lewis Bay), and an inner harbor. The outer and middle harbors are separated by Dunbar Point. Hyannis Harbor is used extensively by recreational boaters and serves as a base for a small fishing fleet, sport fishing charter boats, and ferry boats that service the offshore islands.

Initial work in Hyannis Harbor, completed in 1882, involved building a 1,170-foot-long extension to the existing state-built stone breakwater situated at the southwestern end of the outer harbor in Hyannisport. Work completed by the Corps since that time includes:

• An anchorage 15.5 feet deep behind the 1,170-foot breakwater extension. The anchorage is 1,600 feet long and about 55 acres in area.
• A 7,200-foot-long channel, 12 feet deep and 150 feet wide, extending from the outer harbor to deep water in Lewis Bay.
• A 6,000-foot-long channel, 12 feet deep and 100 feet wide, extending from deep water in Lewis Bay to the town wharf at the western end of the inner harbor.
• An anchorage 12 feet deep at the eastern end of the inner harbor, across from the town wharf.
• Rehabilitation of the 1,170-foot-long breakwater extension.

The state built a 1,000-foot-long stone jetty extending south from Dunbar Point in 1962.