Governors Island is a 172-acre (70 ha) island in Upper New York Bay, approximately 800 yards (732 m) from the southern tip of Manhattan Island and separated from Brooklyn by Buttermilk Channel, approximately 400 yards (366 m). It is part of the borough of Manhattan in New York City. The National Park Service administers a small portion of the north of the island as the Governors Island National Monument, while the Trust for Governors Island operates the rest as a public park. The national historic landmark district, approximately 92 acres (37 ha) of the northern half of the island, is open to the public for several months in the summer and early fall, and the circumferential road around the island is also open to the public. The island is accessed by ferries from Brooklyn and Manhattan.