Named for the beach plums that grew across its sand dunes, records of Plum Island date back to the early 17th century. It was first used as pasture land for livestock by the surrounding colonial towns, who argued for many years for control of the island. The northern tip of the island later served as the building site for a lighthouse in 1787, guiding ships up the mouth of the Merrimack River on their way to Newburyport harbor. It is now controlled largely by the townships of Newbury and Newburyport, the later of which connects to the island by the one bridge across the Plum Island River. Today instead of privateers and fishing ships, the main visitors are nature lovers, bird watchers and vacationers drawn to the unique wildlife and beautiful beaches found on Plum Island.