Green Flats is a reef in City Island Harbor

City Island Harbor

City Island Harbor is the protected body of water between City Island and Hart Island in New York, open to Long Island Sound at its northern and southern extremities. It is not a true harbor, but a Sound. Other minor islands in and around City Island Harbor include the Chimney Sweeps, The Blauzes,...

, between City Island and Rat Island.

The reef is composed of mostly small round glacial alluvial rocks

Rock (geology)

In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

 and a number of glacial erratic

Glacial erratic

A glacial erratic is a piece of rock that differs from the size and type of rock native to the area in which it rests. "Erratics" take their name from the Latin word errare, and are carried by glacial ice, often over distances of hundreds of kilometres...

s made of granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

. It is covered in green seamoss and kelp

Kelp

Kelps are large seaweeds belonging to the brown algae in the order Laminariales. There are about 30 different genera....

. Like all true reefs, it is completely underwater (and a hazard to navigation) at high tide

Tide

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....

 and visible at low tide.

Seagulls take mussel

Mussel

The common name mussel is used for members of several families of clams or bivalvia mollusca, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval.The...

s from the shallows and fly about 30 feet above the reef and drop them and smash the shells on the rocks and then eat the broken up mussels there. Great Blue Heron

Great Blue Heron

The Great Blue Heron is a large wading bird in the heron family Ardeidae, common near the shores of open water and in wetlands over most of North and Central America as well as the West Indies and the Galápagos Islands. It is a rare vagrant to Europe, with records from Spain, the Azores and England...

s may be seen there hunting at low tide.

Local knowledge has it that the reef is getting smaller due to erosion.