U Thant Island (officially Belmont Island) is a small artificial island or islet in the borough of Manhattan in New York City. The island, created during the construction of the Steinway Tunnel directly underneath, is the smallest island in Manhattan. Location and jurisdiction The tiny artificial island is in size and located in the East River, just south of Roosevelt Island. It lies midway between the United Nations Headquarters at 42nd Street, in Manhattan to the west, and Gantry Plaza State Park in Long Island City, within Queens to the east. It is legally part of Manhattan and is formally a part of Manhattan Community District 6, which also includes the neighborhoods of Turtle Bay and Murray Hill to the west of U Thant Island. The island is owned by the New York State Government and is currently protected as a sanctuary for migrating birds, including a small colony of double-crested cormorants. The cormorant population more than doubled from 2000 to 2011. The Borough, Block and Lot is Manhattan, Block 1373 (shared with Roosevelt Island), and Lot 200. Public access is prohibited. Since 2016, the island has been designated a Recognized Ecological Complex under the city's Waterfront Revitalization Program. The reefs in the waters surrounding the island make it a popular spot for boats fishing for striped bass. The United States Coast Guard maintains a 57-foot (17 m) tall lighted beacon on the island, designated "Roosevelt Island Reef Light 17"; an earlier 23-foot (7 m) tall light had been erected in 1938, and another pair before then. Mean sea level in the East River is sometimes measured in reference to the "Belmont Island Datum", 2.265 feet (0.69 m) below that of Sandy Hook. History In the 1890s, businessman William Steinway began a project to construct a tunnel for trolleys under the East River to link Manhattan to his eponymous company town, Steinway Village, in Astoria, Queens; the tunnel would be named the Steinway Tunnel after him. As part of this construction project, a shaft dug into the granite outcrop known as Man-o'-War Reef to reach the tunnels produced excess landfill that built up the reef and created a small island. Steinway died before his tunnels' completion, and financier August Belmont Jr. saw the project to completion between 1905 and 1907. Belmont Island, named after the financier, became the legal name of the island. Four workers were killed in a 1906