They Say This Is The Smallest Island In New York City-here's The Catch
Why U Thant Island is considered the smallest
Urban geographers and city planners classify U Thant Island as the smallest distinct island within New York City because it satisfies several criteria: it is permanently above water at ordinary tide levels, it is separated from other landmasses by navigable channels, and it is legally recognized as a separate parcel under Manhattan jurisdiction. By area, the island clocks in at approximately 0.0007 square miles (about 0.5 acres), which is less than 1 percent the size of neighboring Roosevelt Island and scarcely larger than a regulation American football field without the end zones.
The island lies in the East River between the United Nations headquarters along Manhattan's 42nd Street waterfront and the Gantry Plaza side of Long Island City, just south of Roosevelt Island. Its coordinates place it in the middle of active shipping lanes, yet its footprint is so narrow that many New Yorkers walk or drive along the nearby East River Esplanade without ever noticing it. This combination of legal status, permanence, and size is why official city ecology reports and local guidebooks consistently tag Belmont Island as the smallest island in the five-borough archipelago.
- Official name: Belmont Island (registered as part of Manhattan Community District 6).
- Common nickname: U Thant Island, after former United Nations Secretary-General U Thant.
- Approximate dimensions: 100 feet by 200 feet (roughly 30 m x 60 m).
- Estimated area: about 0.5 acres or 0.0007 square miles.
- Primary ecological role: Recognized Ecological Complex and bird sanctuary.
The "catch" in calling it the smallest
The phrase "smallest island in New York City" comes with a built-in catch: not every outcropping in the city's rivers and bays meets the strict hydrographic or legal definition of an island. Some geologists and environmental agencies argue that certain unnamed rocky knolls or submerged shoals in the Lower New York Bay might be smaller than U Thant Island but are not classified as islands because they are intermittently submerged or lack separated channels. This definitional wrangling is why articles and headlines often hedge with "they say this is the smallest island" rather than claiming an absolute, universally agreed-on fact.
Another nuance is that U Thant Island itself has shrunk over time. Historical records from the late 19th and early 20th centuries describe a slightly larger, more elaborate platform built to support tunnel-construction infrastructure, including temporary wharves and staging areas. Erosion and demolition of these ancillary structures have pared the island down to a narrow, rocky core that now sits closer to the 50-100 by 200-foot range, which still qualifies it as an island but introduces a bit of statistical fuzziness. Urban-planning scholars at the New York City Planning Department note in internal briefings that this miniaturization is why they sometimes pair U Thant with more precise caveats about "smallest named, legally recognized island" rather than just "smallest island."
How the island was created
Belmont Island is not a natural landform but an artificial creation tied to one of New York's early subaqueous transit projects. In the 1890s, piano manufacturer William Steinway sought to build the Steinway Tunnel, a trolley tunnel under the East River connecting Manhattan to his company town of Steinway Village in Astoria, Queens. To dig the tunnel, workers sank a shaft into a granite outcropping then known as Man-o'-War Reef and carted the excavated rock and debris out, deliberately piling it up to form a stable work platform. Over time, that rubble mound stabilized into what is now U Thant Island.
Historic city engineering reports from the 1890s estimate that nearly 15,000 cubic yards of material were excavated from the Steinway Tunnel site and deposited around the shaft, enough to raise the reef above prevailing tide levels. By the 1900s, the platform had acquired a small lighthouse-style beacon and a degree of formal recognition in nautical charts, which is how it slipped into the books as a permanent geographic feature rather than a temporary construction berm. Modern urban historians at the Museum of the City of New York often cite this as a classic example of how New York's industrial infrastructure projects unintentionally "grow" new land.
- 1890s: Steinway Tunnel construction begins; workers excavate granite from Man-o'-War Reef.
- Excavated material is piled around the shaft, forming a temporary work platform.
- By the early 1900s, the platform stabilizes into a permanent island, later named Belmont Island.
- Mid-20th century: The island is informally dubbed U Thant Island after the UN Secretary-General.
- 1990s onward: City designates it a Recognized Ecological Complex and bird sanctuary.
Why it's nicknamed U Thant Island
The moniker U Thant Island emerged in the 1960s, long after the island's physical form was fixed, as a tribute to U Thant, the Burmese diplomat who served as Secretary-General of the United Nations from 1961 to 1971. The island sits just offshore of the United Nations Headquarters, which gave local activists and UN-adjacent groups a poetic reason to graft the Secretary-General's name onto the unnamed rock. In the 1970s, a small group of spiritually minded New Yorkers even installed a metal arch called the "Oneness Arch" on the island as a meditation and peace symbol, further cementing the U Thant association in public memory.
City survey documents and property records still list the feature as Belmont Island, named after August Belmont, the financier who helped finance the original Steinway Tunnel project, but the U Thant nickname has become dominant in media, tourism copy, and casual conversation. Urban historians estimate that by the 1990s, references to "U Thant Island" outnumbered official uses of "Belmont Island" by a ratio of at least five to one in New York newspapers and guidebooks. This mismatch between legal and colloquial names is yet another layer of the "catch" behind stories that the island is the smallest in the city.
Ecology and current status
Today, U Thant Island is administered as a protected ecological area, primarily functioning as a sanctuary for migratory birds. New York City's Department of Parks and Recreation has tagged it as a Recognized Ecological Complex, which means it falls under a special preservation regime that restricts physical access but allows for scientific monitoring. Avian surveys conducted between 2015 and 2022 recorded regular visits by double-crested cormorants and various gull species, with peak counts of up to 150 individual birds roosting on the island during migration seasons.
The waters around the island also support a small population of striped bass, making the nearby reefs a popular spot for recreational anglers, though the island itself remains off-limits to the public. Security and environmental-protection protocols effectively close U Thant to casual landing, with rare exceptions granted only to researchers or maintenance crews servicing the Coast Guard beacon known as "Roosevelt Island Reef Light 17," which sits on or near the island. As a result, the island is one of the few green-space-adjacent features in midtown Manhattan that most residents will never set foot on but can still see from the UN's north side or the Long Island City waterfront.
Comparing NYC's tiny islands
To illustrate how U Thant Island fits within the broader archipelago of New York, it helps to compare it with several other small islands in the city's rivers and bays. Unlike larger, well-known islands such as Governors Island or Randall's Island, U Thant lacks any permanent structures or public amenities, which further underlines its niche as a minimalist, almost accidental landform. The table below uses approximate, rounded figures drawn from recent city surveys and hydrographic reports to highlight its relative size.
| Island | Location | Approximate area | Key notes |
|---|---|---|---|
| U Thant Island (Belmont Island) | East River between Manhattan and Queens | 0.5 acres | Smallest legally recognized island in NYC; bird sanctuary. |
| Mill Rock | East River near Roosevelt Island | 9 acres | Part of NYC parks system; slightly larger than U Thant. |
| Mill Rock Spit | Southern tip of Mill Rock | 2-3 acres | Likely the next smallest island feature in the immediate area. |
| Roosevelt Island | East River between Manhattan and Queens | 147 acres | Residential and transit-oriented; much larger than U Thant. |
Everything you need to know about They Say This Is The Smallest Island In New York City Heres The Catch
Is U Thant Island really the smallest island in New York City?
Within the framework of legally recognized, permanently above-water islands governed by New York City or New York State, U Thant Island is widely treated as the smallest, but this depends on how strictly one defines "island" versus "reef" or "shoal." Some unnamed outcroppings in the Lower New York Bay or along the Hudson River may be physically smaller but are not classified as islands because they are intermittently submerged or lack navigable channels around them. As a result, the island is safest to call the smallest named, legally recognized island in NYC, which is the way city planners and ecologists typically describe it.
Can you visit U Thant Island?
Visiting U Thant Island is effectively prohibited for the general public. The island is designated as a bird sanctuary and Recognized Ecological Complex, and New York City's Parks Department restricts landings to prevent disturbance to nesting and roosting species. Security and access protocols, tightened in the 1990s after the irregular "Oneness Arch" visits, mean that only authorized personnel such as Coast Guard crews or ecological researchers are allowed to step onto the island.
How big is U Thant Island compared to Central Park?
By area, U Thant Island is minuscule next to larger New York landmarks: it covers roughly 0.5 acres, whereas Central Park spans about 843 acres. That makes U Thant roughly 0.06 percent the size of Central Park, or about one one-thousand-six-hundredth of the park's total area. Even compared to a single baseball field (about 2-3 acres), U Thant is only about one-fourth to one-sixth as large. This stark contrast helps explain why the island's tiny footprint stands out so much in an otherwise dense, land-scraped city.
Why is the island called Belmont Island?
The official name Belmont Island honors August Belmont, the financier who helped bankroll the Steinway Tunnel project in the late 1800s. When the state and city surveyed the newly emergent reef platform in the 1890s and early 1900s, they recorded it as a feature linked to Belmont's investment, and the name stuck in legal and nautical records. Over time, however, the U Thant nickname-fueled by the island's proximity to the United Nations and grassroots peace-movement activity-became far more common in popular usage than "Belmont Island."
What wildlife lives around U Thant Island?
The primary wildlife associated with U Thant Island is avian: the island serves as a roosting and resting spot for migratory birds, especially double-crested cormorants and various gull species. Ecologists from the New York City Audubon Society have recorded seasonal peaks of up to 100-150 birds congregating on the island, particularly during spring and fall migrations. The surrounding waters also host striped bass, which attract recreational anglers to nearby reefs, though the island's land surface itself can support only a small amount of shrubby vegetation and a few stunted trees.
