How Wide Is the Long Island Sound?

Spanning the borders of New York and Connecticut, Long Island Sound is an ecologically important east coast estuary. Its bays and inlets wind along coastal communities, adding up to around 600 miles of shoreline. But how wide is Long Island Sound?

The Long and Short of Long Island Sound

If you were to measure Long Island Sound “as the crow flies,” it would only come out to around 110 miles.

But going along the Sound’s unique east-to-west orientation (most large estuaries go north to south), it winds along creating approximately 600 miles of shoreline between both Connecticut and New York.

It’s not all that wide, either! At its broadest area, Long Island Sound is only 21 miles (33 kilometers) wide. Its deepest point is only 65 feet (1981 centimeters). The widest area is at the mouth of the Connecticut River near Old Lyme, Connecticut.

This is why “long, narrow and shallow” are the terms often used to describe Long Island Sound.

An Essential Estuary

Estuaries such as the Sound, which combine fresh water from rivers with saltwater from the sea, are considered the most beneficial of ecosystems. They offer breeding, feeding, nesting, and nursery areas for a wide variety of species. They also provide ideal habitats for some extremely unique life forms, which have the ability to survive and thrive in such an environment.

As the second largest estuary in the U.S., Long Island Sound supports an amazing variety of shellfish, finfish, waterfowl, and plant life. Its waters contain over 170 species of fish, including summer flounder, bluefish, and butterfish, along with 1,200 invertebrates.

The multiple habitats the Sound offers its flora and fauna are a big reason it supports such diversity. These include salt marshes, tidal flats, submerged bottom, and open water. Its eastern end where Connecticut borders Rhode Island is the saltiest part due to its proximity to the Atlantic Ocean.

In 1987 the National Estuary Program recognized Long Island Sound as an “Estuary of National Significance.”

An ‘Urban Sea’

Long Island Sound originates off the New York City boroughs of Queens and the Bronx, at the point where the East River turns into a wider body of water. The southern coastline winds along the length of Long Island to both of its eastern tips. Its northern shore traverses the entire state of Connecticut. On both sides, it forms many bays and inlets.

Due to Long Island Sound’s unique boundaries, it’s also referred to as an “Urban Sea.” That’s because it extends from one of the most densely populated areas on the Eastern Seaboard. It proceeds to meander past cities and towns large and small before opening into the Atlantic Ocean.

It also meanders past several rivers that flow into it from the north. The longest are the Connecticut, the Housatonic, and the Thames, which provide it with 90 percent of its freshwater.

A Bustling Sound

Check a marine radar map of Long Island Sound and you’ll see a busy waterway hosting scores of recreational and commercial vessels. These include ferries, tankers, passenger ships, and tugboats. During days in the summer, it’s estimated that up to 50,000 boats are out on its waters.

As author Tom Anderson pointed out in his book, This Fine Piece of Water, Long Island Sound is the most densely used estuary in North America.

In pre-colonial times you would have also found the shores of the Sound busy, but in another way.

Upwards of 15,000 native Americans made use of the bountiful hunting and fishing along its coastlines and adjacent forests. In 1614 the Dutch continued their exploration of the area with voyager Adriaen Block, marking the first time a European explorer had sailed the entire Sound.

Long Island Sound was now open for the business of trading, and colonists cleared the land for farms and commerce.

A Wide-Ranging Drainage Area

The watershed of Long Island Sound, comprising the land area that drains into it, is extensive. Parts of six states, extending to the Canadian border, are considered to be within its watershed, which has an estimated population of nearly 9 million people.

Low dissolved oxygen conditions are an ongoing threat to aquatic and plant life in the Sound. Nutrient pollution, coming from fertilizer, animal waste, and sewage treatment plants, has been an ongoing concern for decades. This is especially true of the westernmost parts of the Sound. Westchester and Nassau counties in New York and Fairfield County, Connecticut, are where the Sound is at its narrowest and the communities on both coasts are most densely populated.