How Deep Is the Saint Lawrence River?

Written by Kyle Glatz
Updated: July 2, 2023
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Key Points

  • The Saint Lawrence River’s source is located in Lake Ontario. The river begins near Kingston, Ontario in Canada, and Cape Vincent, in New York.
  • The Saint Lawrence River is 250 feet deep at its greatest depth.
  • The river was used many times throughout history to capture important areas, including during the Seven Years’ War.

The Saint Lawrence River is a long, wide river that some people mistakenly believe to be a source of the Great Lakes’ water. However, the water runs from the Great Lakes out to the Atlantic Ocean. The river is a very important part of the Great Lakes Waterway, allowing cargo to travel to inland cities like Chicago and Toronto, thousands of miles inland. The river channel has to be fairly deep to facilitate such travel. So, how deep is the Saint Lawrence River?

Find out how deep this river goes, learn about its history, and find out what animals live along this amazing body of water!

Where Is the Saint Lawrence River?

Kingston, Ontario Canada

Kingston, Ontario sits on Lake Ontario.

©cvrestan/Shutterstock.com

The Saint Lawrence River’s source is located in Lake Ontario. The river begins near Kingston, Ontario in Canada, and Cape Vincent, in New York. The river runs for a total length of about 743.8 miles from Lake Ontario to the Atlantic Ocean. However, if counting the farthest headwaters in Minnesota, then the length would be about 1,900 miles. By that measure, it’s the third-longest river in Canada!

The river acts as a natural border between the United States and Canada for a lot of its length. However, once it passes Cornwall, it only flows in Canada. Along the way, the true river reaches many cities like Montreal and Quebec City.

A History of the River

Iroquois Artifacts on display at a reconstructed 15th century Iroquois village

Iroquois artifacts on display at a reconstructed 15th-century Iroquois village.

©iStock.com/skyF

The history of the Saint Lawrence River is long and storied. Many Indigenous people lived along its banks for centuries. Norse explorers also sailed through the Gulf of St. Lawrence, but they did not settle in the region.

Jacques Cartier became the first European to sail up the river. Eventually, more Europeans followed, and they traded with the Iroquoians that lived nearby.

The river was used many times throughout history to capture important areas, including during the Seven Years’ War. And most recently during the Second World War. Today, the river is used as a place of transportation and commerce. The Canadian and United States of America have worked together to make the river navigable far inland. Dredging, canal building, and mapping of the area have allowed this vital commercial vein to facilitate billions of dollars in economic activity each year.   

Although this is not the longest river or the widest, it’s still one of the most important for commerce in North America.

How Deep is the Saint Lawrence River?

A view of the St. Lawrence River from Wellesley Island State Park

A view of the St. Lawrence River from Wellesley Island State Park near the deepest part of the river.

©iStock.com/Eric Bardo

The Saint Lawrence River is 250 feet deep at its greatest depth. That makes this river one of the deepest in North America. The Hudson River is the deepest river in the United States, and it measures between 202 and 216 feet deep depending on the source used for the information.

The deepest part of the river is found in an area of the river called the American Narrows in the Thousand Islands region of the river.

The deepest depth is found north of Vanderbilt Island, near the coast of Wellesley Island. According to recent river measurements from the NOAA Office of Coast Surveys, the depth in this part of the water varies from 239 to 250 feet.

This part of the river may sound familiar to some people. After all, the famous NEPCO-140 oil barge ran aground in 1976, dumping about 300,000 gallons of crude oil into the water. This occurred off the coast of Clayton, just south of Wellesley Island.

The Thousand Islands region of the river, especially the American Narrows, is deep but narrow with difficult terrain on either side. The area requires great care on the part of the ship pilots to safely navigate.

What Animals Live in the Saint Lawrence River?

Canada geese

Canada geese are a common sight on this river.

©iStock.com/yujie chen

The St. Lawrence River stretches for 743.8 miles. The river’s ecosystem houses all sorts of different animals. The land surrounding the water and the river itself are brimming with life. Some of the animals that live in the area around the St. Lawrence River include:

These are just a few of the animals that people see close to the river.

Of course, the St. Lawrence River is home to many species of fish, reptiles, and amphibians. Some of the creatures that live in the water include:

People that go fishing along this body of water enjoy the bountiful number of species available. However, the river’s specialty is bass. In fact, the St. Lawrence River is considered one of the best places to catch bass in North America.

All told, the ecology of the St. Lawrence River is thriving, but it still faces some threats. Continued economic activity could lead to further pollution of the waterway. However, authorities in the region do everything they can to limit the chances of oil spills or other problems in the region.

Conclusion

While some parts of the river are shallow, the shipping channels of the Saint Lawrence River are fairly deep. They are purposely kept deep to allow for economic activity to occur in the area. The deepest part of the river is found less than 100 miles upriver from Lake Ontario, and it plunges 250 feet deep. Aside from shipping, the river also helps support diverse wildlife in the region. Many animals thrive on the islands and shores of this river, and all sorts of fish live in its waters.

The photo featured at the top of this post is © R.M. Nunes/Shutterstock.com


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About the Author

Kyle Glatz is a writer at A-Z-Animals where his primary focus is on geography and mammals. Kyle has been writing for researching and writing about animals and numerous other topics for 10 years, and he holds a Bachelor's Degree in English and Education from Rowan University. A resident of New Jersey, Kyle enjoys reading, writing, and playing video games.

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