How big is Lake Ontario?

Lake Ontario, though the smallest by surface area among North America's five Great Lakes, is anything but minor in its importance and grandeur. Nestled between the Canadian province of Ontario and the U.S. state of New York, this impressive body of water has played a vital role in shaping the economy, ecosystems, and history of the surrounding region. But just how big is Lake Ontario? Let’s dive deep into the numbers—and the significance behind them.

Size and Dimensions of Lake Ontario

1. Surface Area

Lake Ontario covers an impressive surface area of approximately 7,340 square miles (19,000 square kilometers). While it is the smallest of the Great Lakes by area, it is still larger than many entire countries and states, including nations like Slovenia or states like New Jersey.

2. Length and Width

The lake stretches about 193 miles (311 kilometers) in length from east to west and spans roughly 53 miles (85 kilometers) at its widest point from north to south. Its elongated shape gives it a distinctive, narrow profile compared to the other, more rounded Great Lakes.

3. Depth

Lake Ontario is notably deep. It has an average depth of 283 feet (86 meters), but its deepest point plunges to an astonishing 802 feet (244 meters). That makes it the second deepest of the Great Lakes, just after Lake Superior. In fact, much of Lake Ontario’s bottom lies below sea level, a feature created by the same glacial forces that shaped the entire Great Lakes basin.

4. Volume

The lake holds about 393 cubic miles (1,639 cubic kilometers) of water. That’s more than enough to cover the entire state of New York in a few feet of water! Although smaller in surface area, Lake Ontario’s depth gives it a massive volume of fresh water, crucial for ecosystems and human consumption.

5. Shoreline

Lake Ontario’s shoreline, excluding islands, stretches for about 712 miles (1,146 kilometers). Its coastlines are lined with bustling cities, charming towns, parks, beaches, and natural reserves.

How Lake Ontario Compares to Other Great Lakes

While Lake Ontario is the smallest in terms of area, it remains vital when compared to its larger siblings:

• Lake Superior: 31,700 square miles
• Lake Huron: 23,000 square miles
• Lake Michigan: 22,400 square miles
• Lake Erie: 9,910 square miles
• Lake Ontario: 7,340 square miles

Interestingly, Lake Ontario’s depth makes it more voluminous than Lake Erie, despite being smaller in surface area. Lake Erie, although larger by area, is the shallowest Great Lake and holds much less water than Lake Ontario.

Geographic and Environmental Significance

Lake Ontario serves as the outlet of the Great Lakes Basin, where water from the other lakes flows through the Niagara River and over Niagara Falls before reaching Lake Ontario. From there, water continues its journey into the St. Lawrence River and eventually to the Atlantic Ocean.

Because of its position at the end of this great water chain, Lake Ontario plays a critical role in regulating water levels for the entire basin. It is also heavily monitored for environmental health, especially regarding pollution control, invasive species management, and climate change impacts.

The lake’s size and location create a unique microclimate along its shores, often referred to as the "Lake Ontario snowbelt." In winter, cold winds moving across the warmer lake waters produce heavy snowfall inland, particularly on the southern and eastern shores.

Cities and Populations Around the Lake

Lake Ontario's size supports a densely populated and highly developed region. Major cities along its shores include:

Toronto, Ontario — Canada's largest city and a major global metropolis.

Hamilton, Ontario — An industrial and cultural center.

Kingston, Ontario — A historic city at the lake’s eastern gateway to the St. Lawrence River.

Oshawa, Ontario — A dynamic city evolving beyond its automotive roots.

Rochester, New York — A historical American city known for innovation and the arts.

In total, millions of people live in the Lake Ontario watershed, relying on it for drinking water, transportation, agriculture, recreation, and industry.

Final Thoughts: A Small Giant Among the Great Lakes

Lake Ontario might be the "smallest" Great Lake in terms of surface area, but its scale remains vast and its importance immense. Its deep waters hold an incredible volume of freshwater, support vibrant communities, and nurture diverse ecosystems. Whether you're marveling at Toronto's skyline, sailing off the shores of Rochester, or hiking along the Scarborough Bluffs, you're experiencing the greatness of Lake Ontario—a true giant in both natural beauty and ecological significance.