Lake Ontario facts for kids

Kids Encyclopedia Facts

Quick facts for kids Lake Ontario
Lake Ontario seen from the International Space Station. The light patches show an algal bloom.
Lake Ontario Location in North America
Depth map of Lake Ontario. The deepest spot has an "×" mark.
Location	North America
Group	Great Lakes
Coordinates	43°42′N 77°54′W / 43.7°N 77.9°W / 43.7; -77.9
Lake type	Glacial
Etymology	Ontarí:io, a Wyandot word meaning "great lake"
Primary inflows	Niagara River
Primary outflows	St. Lawrence River
Catchment area	64,020 km² (24,720 sq mi)
Basin countries	Canada United States

Max. length	311 km (193 mi)
Max. width	85 km (53 mi)
Surface area	19,000 km² (7,340 sq mi)
Average depth	86 m (283 ft)
Water volume	1,631 km³ (391.4 cu mi)
Residence time	6 years
Shore length¹	1,146 km (712 mi)
Surface elevation	74 m (243 ft)
Settlements	Toronto, Mississauga, Hamilton, Rochester
¹ Shore length is not a well-defined measure.

Lake Ontario is one of the five famous Great Lakes found in North America. It sits proudly along the Canada–United States border, separating two friendly nations. To its north, west, and southwest lies the Canadian province called Ontario. To its south and east lies the U.S. state of New York. Many bustling cities sit on its shores, including Toronto, Mississauga, Hamilton, St. Catharines, and Kingston in Canada. On the American side, you can find the cities of Rochester and Watertown.

This great body of water is the very last lake in the massive freshwater chain. Water rushes in from Lake Erie through the powerful Niagara River. It then exits the lake through the mighty St. Lawrence River and travels directly to the Atlantic Ocean. Giant ships carry goods through the lake along the busy St. Lawrence Seaway. Huge structures like the Moses-Saunders Power Dam help keep the water levels steady. Lake Ontario is filled with fascinating wildlife, exciting human history, and wonderful natural wonders.

Learning About the Lake Name and Meaning
Geography and Size of Lake Ontario
Geology and How the Lake Formed
Climate and Weather Wonders
Ecology and Protecting Wildlife
Human History and Amazing Adventures
- Brave Swimmers Crossing the Lake
Towns, Cities, and Island Havens
Navigating the Waters and Historic Lighthouses
Preserving History: The National Marine Sanctuary
Modern Economy and Busy Harbors
Images for kids
See also

Learning About the Lake Name and Meaning

The name Ontario comes from an ancient First Nations language. Experts believe it comes from the Iroquoian words Kaniatarí:io or Oniatarí:io. These words mean "lake of shining waters" or "beautiful lake". People have used this pretty name for hundreds of years, since at least 1641. Long ago, the Wyandot people also used a word that meant "great lake".

European explorers gave the lake several other names when they first arrived. A French explorer named Samuel de Champlain called it "Lac S. Louis" in 1632. People used that name until near the end of the 17th century. During the era of French colonial Canada, leaders also called it Lac Frontenac. However, the lovely local name Ontario was the one that stayed popular. In 2026, American political leaders suggested calling it 'Lake America' during trade discussions. Map apps like Apple Maps and Google Maps made updates, but the world still knows this magnificent lake as Lake Ontario.

Geography and Size of Lake Ontario

Lake Ontario's drainage basin

Lake Ontario is the easternmost lake of the five Great Lakes. In surface area, it is the smallest of the group. It covers an area of about 19,000 square kilometres [7,340 sq mi]. Even though it covers less surface area than Lake Erie, it actually holds much more water. Its deep basin gives it a volume of 1,640 km³ [393 cu mi]. In fact, it ranks as the 13th-largest lake in the entire world.

The shoreline stretches for 1,146 kilometres (712 mi) when you include all of its lovely islands. Lake Ontario has an average depth of 86 metres [283 ft]. Its deepest spot drops down to 244 metres [802 ft] in the Rochester Basin. Because it sits at the end of the Great Lakes system, it has the lowest elevation. Its surface is 74 metres (243 ft) above sea level. That is 99 metres (326 ft) lower than Lake Erie, which sits right upstream.

The surrounding drainage basin collects water from a land area of 64,030 square kilometres (24,720 sq mi). Water levels naturally rise and fall throughout the different seasons. These regular shifts help the lake ecology stay balanced and healthy. Shifting water levels keep coastal marshes wet, which provides homes for countless animals. Unfortunately, problems like overfishing and pollution have harmed fish populations over time. Harmful invasive species have also caused trouble for the native creatures.

Natural sand barriers called baymouth bars run along several parts of the coast. These sandy ridges form calm lagoons and safe harbors for boats. A famous example is Toronto Bay, which sheltered early ships in Upper Canada. Other protected waters include Hamilton Harbour, Irondequoit Bay, Presqu'ile Bay, and Sodus Bay. Many of these bars have sunny sandy beaches, like those at Sandbanks Provincial Park and Sandy Island Beach State Park.

A special natural landmark on the Canadian side is the Z-shaped Bay of Quinte. It separates Prince Edward County from the mainland, connected only by a narrow land strip. Many different waterways feed into Lake Ontario every single day. Famous Canadian rivers include the Don River, Humber River, Rouge River, Trent River, Cataraqui River, Credit River, and Ganaraska River. Famous American rivers include the Genesee River, Oswego River, Black River, Little Salmon River, and the Salmon River. Ships can skip past the giant waterfall on the Niagara River by traveling through the engineered Welland Canal.

Geology and How the Lake Formed

The deep basin of Lake Ontario was carved out during the last ice age. Massive sheets of moving ice, called the Wisconsin ice sheet, crushed soft Silurian rocks. As the heavy glacier crawled southward, it carved out the ancient Ontarian River valley. The moving ice carried tons of rocky dirt, called glacial till, across the land. This dirt formed hills called drumlins, kames, and moraines.

When the climate warmed, the glacier slowly began to melt away toward the north. The ice blocked the St. Lawrence river valley like a giant plug. This trapped the meltwater and created a super-sized ancient lake called Lake Iroquois. Because the water was trapped, it was much higher than the lake we see today. The ancient lake drained south near Syracuse, New York, flowing into the Mohawk River and Hudson River. You can still see old, dry beaches and wave-carved hills miles away from the current shoreline.

Eventually, the wall of ice melted away from the St. Lawrence outlet. Because the land had been crushed down by heavy ice, the lake briefly connected to ocean saltwater. This salty stage was known as the Champlain Sea, forming an inland bay. Over thousands of years, the land slowly pushed back upward in a process called post-glacial rebound. The land around the St. Lawrence outlet is still rising about 30 centimetres (12 in) every century. Because the northern end is rising faster, the water tilts toward the south, turning river valleys into bays and eroding shores.

Climate and Weather Wonders

Hamilton Harbour frozen over. Ice sheets can form along the shoreline of Lake Ontario during the winter.

Lake Ontario experiences a rhythmic water slosh called a seiche, rocking back and forth every eleven minutes. Wind and sudden air pressure changes can push this rocking wave even higher. Because Lake Ontario is extremely deep, the entire lake almost never freezes completely during winter. Instead, floating ice sheets cover between 10% and 90% of the surface. Ice always forms first in shallow bays and along the calm edges. The lake has frozen entirely across on only five recorded occasions: in 1830, 1874, 1893, 1912, and 1934.

Winter winds blowing from Canada pick up moisture over the warm lake water. When this damp air hits the colder land, it drops huge piles of lake-effect snow. The southern and eastern shores sit directly in this stormy path, known as the snowbelt. Small towns like Oswego and Pulaski can receive more than twenty feet of snow each winter. The elevated Tug Hill Plateau receives more snow than almost any other spot in the eastern United States. Snow lovers flock to Tug Hill to ride snowmobiles and enjoy cross-country skiing.

The snowy weather regularly reaches as far inland as Syracuse. That city often records the most snowfall of any major American city. Other chilly cities around the world get even more snow, like Quebec City and snowy Sapporo in Japan. In autumn, warm lake water meeting chilly air often creates thick blankets of blinding fog.

The lake also creates a friendly microclimate that helps farmers grow delicious fruit. Cool breezes in the spring stop fruit trees from budding too early before frosts finish. In autumn, the warm water prevents early freezes, extending the growing season. Farmers grow lots of juicy apples, cherries, pears, plums, and peaches around Rochester. The Niagara Peninsula and Stoney Creek are famous for great fruit orchards. On the southern side, orchards stretch into Niagara and Orleans counties in New York. Across the lake, tough apple varieties grow very well around Cobourg.

Ecology and Protecting Wildlife

Profile of coastal wetlands for Lake Ontario

The lands and waters around Lake Ontario are bursting with biodiversity. A wide range of birds, fish, frogs, turtles, and colorful wild plants make their home here. The sandy beaches, sheltered bays, and soggy wetlands are essential habitats for these animals. Many coastal wetlands enjoy special legal protection to keep them safe from harm.

When humans control water levels, delicate plants in a wet meadow can struggle to reproduce. Cattails from the Typha plant family often crowd out the native marsh flowers. Extra plant nutrients entering the water can trigger eutrophication, causing weeds to grow out of control. Sandy hollows behind dunes form special wetland pools called pannes. Places like Presqu'ile boast many unusual and rare plants in these wet hollows.

Lake Ontario's food web

The surrounding forests belong to a deciduous forest biome, filled with maple, oak, and beech trees. Canadian scientists group this region into the Mixedwood Plains Ecozone, studied by Environment and Climate Change Canada. American scientists describe it as the Eastern Great Lakes and Hudson Lowlands through the United States Environmental Protection Agency. Past logging removed much of the original forest cover, which harmed wild birds and river fish. Conservation teams now work hard to plant native trees along streams to restore the natural woodland.

In past decades, heavy chemical pollution caused slimy algal blooms to coat the shoreline during summer. These green blooms sucked oxygen out of the water, harming local fish. Because Lake Ontario sits at the end of the Great Lakes system, it catches leftover pollution from upstream. Pollutants have entered the water through aging city sewage systems and factory drains. However, communities have built great cleanup projects. A famous industrial area called Randle Reef received a major 150-million-dollar cleanup to restore clean water.

Human History and Amazing Adventures

Archaeologists know that humans have lived near Lake Ontario for roughly 11,000 years. Early hunters followed herds of caribou and gathered wild plants along the ancient shores. As centuries passed, the lake became a natural border between the Wendat and the Haudenosaunee Confederacy. In the 1600s, groups of Haudenosaunee built towns along the north shore. Later, the Anishinaabe people moved into the region and continued using the traditional Iroquois lake name.

A map depicting the Haudenosaunee settlement of the north shore of Lake Ontario during the late-17th century

A French traveler named Étienne Brûlé was likely the first European person to view the lake in 1615. European explorers wrote down stories about a legendary lake creature called Gaasyendietha. This mythical dragon was said to shoot fire and swim through the deep water like a giant serpent. Soon, European traders arrived to build military forts and fur trading posts. Famous spots included Fort Frontenac, built in 1673, Fort Oswego in 1722, and Fort Rouillé in 1750.

During the American Revolution, the British military held strong control over the lake. Many families who supported the British crown, called Loyalists, moved across the water to build new homes in Canada. Under the Jay Treaty of 1794, the United States gained control of the forts on the southern shore.

USS General Pike and HMS Wolfe prepare for action on September 28, 1813. The battle was one of several engagements that took place on Lake Ontario during the War of 1812.

During the War of 1812, both countries built large wooden warships to control the waters. American shipbuilders worked at Sackets Harbor, while British workers built ships at Kingston. Several brave naval battles took place out on the open lake. When the conflict ended, both nations signed the Rush–Bagot Treaty in 1818. This historic agreement removed warships from the Great Lakes, ensuring peaceful borders ever since.

After peace returned, trading schooners and wooden steamships filled the lake. The very first steamer on the Great Lakes was the Frontenac, launched near Kingston in 1816. American builders launched the steamship Ontario just a few months later. Soon, engineer John Ericsson designed new screw propellers to power cargo ships like the historic Vandalia. Workers near Port Credit also practiced stonehooking, gathering flat shale stone from the lake floor to build houses in Toronto.

Brave Swimmers Crossing the Lake

Marilyn Bell Park in Toronto

Swimming across Lake Ontario is a world-famous challenge for endurance athletes. More than 60 skilled swimmers have crossed the chilly waters safely. The very first person to accomplish this amazing swim was 16-year-old Marilyn Bell in 1954. She battled cold waves and lamprey eels to reach Toronto. The city honored her courage by opening Marilyn Bell Park on the lakefront.

In 1974, a famous swimmer named Diana Nyad became the first person to cross from north to south. Young people have also set incredible swimming records. In 2007, 14-year-old Natalie Lambert completed the swim in less than 24 hours. In 2012, 14-year-old Annaleise Carr became the youngest swimmer to make the 52-kilometer crossing, finishing in just under 27 hours.

Towns, Cities, and Island Havens

View of Toronto and a frozen Lake Ontario from the Toronto Islands. Toronto is the largest settlement located along the lake's shoreline.

The western end of the lake is home to an enormous urban area called the Golden Horseshoe. Nearly 9 million people, which is over a quarter of Canada's total population, live within this lake basin. In contrast, the American side is much more rural, with roughly two million people living in its watershed.

Notable settlements along the shoreline include:

View of Stella Village on Amherst Island, one of several islands located in the lake

Lake Ontario is dotted with scenic islands, mostly located near the northeastern exit. These islands sit upon ancient rock formations known as geological basement rock. The largest island in the entire lake is Wolfe Island, located near Kingston.

Other notable islands include:

Navigating the Waters and Historic Lighthouses

Canal Lock 1 at the Welland Canal in Lake Ontario. The canal forms a part of the Great Lakes Waterway, which connects Lake Ontario with the St. Lawrence River and other Great Lakes.

The lake serves as a vital shipping path through the Great Lakes Waterway. Huge cargo ships can travel from the Atlantic Ocean into the Great Lakes heartland. Smaller pleasure boats can travel to Georgian Bay through the Trent-Severn Waterway via Lake Simcoe. In New York, the Oswego Canal connects the lake to the New York State Canal System, reaching Lake Erie and Lake Champlain. Boaters can also travel up the historic Rideau Canal from Kingston all the way to Ottawa.

Historic lighthouses were built along the rocky shores to help ship captains navigate safely through the dark. Some famous historic lighthouses include:

Braddock Point Light
Charlotte-Genesee Lighthouse
Gibraltar Point Lighthouse
Oswego Harbor West Pierhead Light
Presqu'ile Lighthouse
Selkirk Lighthouse
Sodus Point Light
Stony Point Light
Thirty Mile Point Light

Road travelers can also explore the lake from the shore. The Great Lakes Circle Tour and Seaway Trail create a fun scenic driving route along the coastline.

Preserving History: The National Marine Sanctuary

A 2024 map of the Lake Ontario National Marine Sanctuary

In September 2024, the United States established the Lake Ontario National Marine Sanctuary. This protected zone covers 1,300 square nautical miles; 4,460 square kilometres (1,722 sq mi) of water in the southeastern part of the lake. The national marine sanctuary protects dozens of historic wooden shipwrecks resting peacefully on the lake bottom. The sanctuary is also important for honoring the sacred heritage of the Haudenosaunee Confederacy. The sanctuary is managed jointly by the Office of National Marine Sanctuaries and the Government of New York.

Modern Economy and Busy Harbors

Cargo ships in Oshawa Harbour

Lake Ontario remains an engine of economic trade for both Canada and the United States. Busy commercial shipping docks operate at the Port of Toronto and the Port of Hamilton. Hamilton Harbour is also well known for producing steel used in buildings and cars.

Years ago, the Great Lakes supported an enormous commercial fishing fleet. Because too many fish were caught, commercial fishing ended. Today, millions of visitors enjoy recreational sports fishing on the lake, casting lines for salmon and trout. Lake Ontario continues to be an incredible natural treasure that provides drinking water, clean recreation, and natural beauty to millions of people.

Images for kids

Lake Ontario's beachfront in Rochester, New York