U Thant Island

U Thant Island (officially Belmont Island) is a small artificial island or islet in New York City's East River, within the borough of Manhattan. The 100-by-200-foot (30 by 60 m) island, created during the construction of the Steinway Tunnel directly underneath, is the smallest island in Manhattan. The island is named after August Belmont Jr., who financed the construction of the subway tunnel, and in 1977 was dedicated to the memory of U Thant, the former Secretary-General of the United Nations. The islet contains a lighted beacon marking the southern end of Roosevelt Island Reef and is the home to a small colony of double-crested cormorants.

The tiny artificial island is 100 by 200 feet (30 by 60 m) 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 Borough, Block and Lot is Manhattan, Block 1373 (shared with Roosevelt Island), and Lot 200.

The island is owned by the New York State Government and is currently protected as a sanctuary for migrating birds. Public access is prohibited. Since 2016, the island has been designated a Recognized Ecological Complex under the city's Waterfront Revitalization Program.

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. Belmont Island is located near the southwest end of Roosevelt Island Reef, which extends 0.3 nautical miles (0.3 mi; 0.6 km) southwestward from Roosevelt Island.

Elevations on Roosevelt Island are sometimes measured in reference to the "Belmont Island Datum", which is 2.265 feet (0.69 m) below the mean sea level at Sandy Hook.

In the 1890s, businessman William Steinway began a project to construct a tunnel for trolleys under the East River to link Manhattan to his company town, Steinway Village, in Astoria, Queens; the tunnel would be named the Steinway Tunnel after him. Work on the project was halted in 1892 after a dynamite blast near a shaft in Long Island City killed five workers. Steinway died before his tunnels' completion, and financier August Belmont Jr. saw the project to completion between 1905 and 1907. The tunnels, which pass directly beneath the island, are now part of the New York City Subway system and used by the IRT Flushing Line (7 and <7>​ trains). A shaft dug into the rock outcrop known as Man-o'-War Reef during construction of the tunnel produced excess landfill that built up the reef and created a small island. Belmont Island, named after the financier, became the legal name of the island.

From 1899 to 1903, the portion of the rock ledge that extended southwestward from Blackwell's Island known as Man-o'-War Rock had been blasted to a depth of 26 feet (7.9 m) for the federal government; the southern end of this reef was located across from East 37th Street in Manhattan. Two other groups of rocks were located between Man-o'-War Rock and Blackwell's Island. According to William Barclay Parsons, who worked on the Steinway Tunnel as a consulting engineer, and Colonel H. Taylor of the Corps of Engineers, the location of the shaft was incorrectly referred to as "Man-of-War-Reef" and the rock outcrop was instead located near the southern end of "Blackwell's Island Reef." Parsons noted that the site of the shaft was commonly called Man-of-War Reef even though that reef had been removed by the federal government. The rock outcrop the shaft was located on, along with Blackwell's Island, were both composed of Fordham gneiss.

Permission to construct two shafts on Man-o'-War Reef and create a temporary island to support the staging of equipment was obtained from Robert Shaw Oliver of the War Department on June 28, 1905. The permit was effective for a two-year period beginning on July 1, 1905 and allowed a temporary island up to 100 feet (30 m) wide by 400 feet (120 m) long to be created. At the conclusion of the work, the equipment was to be removed and the rock outcrop was to be returned to its original condition. A similar permit was obtained from the Commissioners of the Land Office of New York State on July 8, 1905. Permission to sink a shaft in the East River had originally been requested from the Corporation Counsel, which referred the matter to the Commissioner of Docks and Ferries, but no records of grants of land under water from the state to the city were found in the vicinity of the proposed shaft site, which prompted the Corporation Counsel to advise the Attorney General of New York of the matter. Authorization was also received from the Lighthouse Service to temporarily move the Blackwells Island Reef light located on Man-o'-War Rock to the top of a building that was constructed on the island.