Lake Ontario ecosystem

• Category: Inland Aquatic Biomes
• Geographic Location: North America
• Summary: Smallest of the North American Great Lakes in surface area, and third-largest in total volume of water, Lake Ontario has suffered from human activity since the arrival of the earliest European settlers.

Étienne Brûlé, the young scout of French explorer Samuel de Champlain, was the first European to see Lake Ontario in 1615, and a few months later, he guided Champlain to the lake. Ontario stems from a Huron word meaning "sparkling water."

Lake Ontario is, by surface area, the smallest of the North American Great Lakes and the thirteenth-largest lake in the world. The lake forms an international boundary between the United States and Canada. It is bounded on the north and southwest by the Canadian province of Ontario, and on the south, New York State forms the boundary with the United States. Lake Ontario is the only Great Lake that is not in part bordered by the state of Michigan.

Lake Ontario is the last in the Great Lakes chain; it serves as the outlet to the Atlantic Ocean for the waters of all the lakes. The lake lies 243 feet (74 meters) above sea level and 325 feet (99 meters) below Lake Erie. Water that begins its voyage in Lake Superior flows through Lake Erie, over Niagara Falls, and down into Lake Ontario, where it joins the Saint Lawrence River and finally mixes with the Atlantic Ocean.

Lake Ontario is 190 miles (310 kilometers) long and 53 miles across (85 kilometers) at its widest point. Its average depth is 283 feet (86 meters), and it reaches a maximum depth of 802 feet (244 meters). Lake Ontario has a water-retention time of six years, nearly three times that of Lake Erie. The shoreline of Lake Ontario is the shortest of all the Great Lakes, extending for only 712 miles (1,146 kilometers), including its islands. Lake Ontario holds a large proportion of cold bottom waters and is mesotrophic, meaning its nutrient load is less than that of eutrophic Lake Erie, but greater than that of the mainly oligotrophic Lakes Superior, Michigan, and Huron.

Its watershed includes parts of Ontario, New York, a small portion of Pennsylvania, the incoming Niagara River, Niagara Falls, and numerous other lakes and streams that empty into the lake before all the waters discharge into the St. Lawrence River.

Major urban industrial centers, such as Toronto and Hamilton, Ontario, are located on its western shore. The Canadian shoreline of Lake Ontario is densely populated and heavily urbanized, while its United States shoreline is, for the most part, sparsely populated and used mainly for farmland and resorts.

Lake Ontario has been exploited longer than any of the other Great Lakes, first by lumber mills and commercial fisheries, and later by agriculture and industries. Industry and agriculture have added nutrients to the shallower regions of the lake, resulting in making Lake Ontario a mesotrophic lake with more oligotrophic deep basins.

Because of its great depth, the lake as a whole never freezes in winter, but an ice sheet covering between 10 and 90 percent of the lake area typically develops, depending on the severity of the winter. When cold winds pass over the warmer water of the lake, they pick up moisture and precipitate it as lake-effect snow. Because most of the winds are from the northwest, the southern and southeastern shoreline of the lake is referred to as the snowbelt, and may receive up to 20 feet (600 centimeters) or more of snow.

Lake Ontario is mainly in the humid continental climate zone. This region has warm and sometimes hot summers with colder, longer winters, and ample snowfall. Average daily maximum and minimum temperatures in Toronto in July are, respectively: 80 degrees and 64 Fahrenheit (26 and 18 Celsius); and for January: 30 and 19 Fahrenheit (minus 1 and minus 7 Celsius).

Wildlife

Lake Ontario has an extensive dune system stretching for seventeen miles (twenty-seven kilometers) along the New York coastline. Dune systems here support more unique species of plants and animals than any other ecosystems in the Great Lakes region. These dunes are composed of sand that was deposited in the basin by the melting glaciers 10,000 years ago. This sand is transported by wind and water to the lake shoreline, where plants such as marram grass (Ammophila breviligulata) helps trap the sand and begin dune formation.

The dunes of the Great Lakes basin support more than 3,500 species of vascular plants, mammals, birds, and fish, as well as numerous insects and fungi. Of note, naturalist Henry Cowles’s studies of succession at the Indiana Dunes, along the eastern coast of Lake Michigan, provided the first truly scientific look at how succession works and how the environment affects plant-community structure.

Lake Ontario and its shores provide a stopover for many migratory bird species. Millions of songbirds will travel here from the tropics each spring and nest, then return to southern regions of the United States, Mexico, Central America, the Caribbean, and South America. Some of the bird species found here include warbler, oriole, tanager, flycatcher, thrush, loon, grebe, goose, merganser, gull, tern, and petrel. Birds that are endangered or threatened in the Lake Ontario region include the black tern, pied-billed grebe, least bittern, American bittern, and northern harrier. Large flocks of swallows, including bank swallows, are also known to migrate through the area.

The lake provides a critical habitat and migration area for shorebirds, songbirds, and waterfowl in the form of inland dunes and wetlands with extensive barrier beaches backed by shrub and forested lands. There are some rare or exemplary ecological communities: silver maple-ash swamp, rich shrub fen, medium fen, red maple-hardwood swamp, red maple-tamarack peat swamp, maple-basswood forest, and deep emergent marsh.

Lake Ontario was once home to the landlocked Atlantic salmon (Salmo salar), but less than a century after European settlement, a resource that seemed limitless had all but vanished from the lake. The species was revered by the Indigenous peoples living near the lake, and was an important part of their diet. European settlers were already familiar with this fish, and not long after settlements were established, commercial and recreational fisheries for Atlantic salmon developed on the lake. Average sizes of 18 inches (46 centimeters) and 2 to 4 pounds (0.9 to 1.8 kilograms) were probably typical in the historical population of Lake Ontario, and historical records suggest that fish up to almost 45 pounds (20 kilograms) were occasionally caught. Habitat loss due to lumber mills along the streams, overfishing, and pollution led to the extirpation of this important native species by 1898.

After a series of failed recovery efforts beginning in the early twentieth century, a reintroduction program was initiated in 1985 by the New York State Department of Environmental Conservation (DEC). Recovery efforts appeared to be working, and more than a century after the last harvest of these fish, the Atlantic salmon returned to Lake Ontario. A 35-inch, 24.3-pound (89-centimeter, 11-kilogram) fish caught in 1989 is the modern-day Ontario record for the species. However, Atlantic salmon conservation issues continued into the first decades of the twenty-first century. The New York DEC's Lake Ontario Atlantic Salmon Fisheries Management Plan 2023-2026 outlined several challenges limiting Atlantic salmon populations, including competition with Pacific salmon, a lack of suitable summer habitat, difficult data collection conditions for conservationists, limited stocking and hatchery capacities, and the lack of fish that meet the nutritional needs of Atlantic salmon.

Other fish in the original Lake Ontario food web include lake trout; lake whitefish; and bloater chub, a species once abundant in the deeper water of the lake, along with the lake sturgeon, which fed on the bottom with a specially adapted suctionlike mouth. This feeding niche is now occupied by a nonnative fish, the carp, which can tolerate more pollution and is more prolific. The kiyi, a subspecies of cisco, was declared extinct in 2005. As species were lost, others immigrated and took their places. Alewives and rainbow smelt from the Atlantic have replaced the similarly planktivorous lake herring. Smallmouth, pumpkinseed, and rock bass live around the islands and shallow shoals in the eastern portion of the lake, feeding on minnows, frogs, and insects. Even these natives have been replaced by carp and other invaders as pollution and climate change alter the environment.

Freshwater eels are important scavengers in Lake Ontario. They eat a variety of species and help keep populations balanced. Their life cycle is the reverse of the Atlantic salmon—they spawn in the Sargasso Sea in the Atlantic, hatch, and migrate up the Gulf Stream to the St. Lawrence River and on into Lake Ontario. Some even make it into other Great Lakes. When it is time to spawn, they make their way back to the St Lawrence and out to the Atlantic. Because of their feeding habits, they pick up large amounts of toxins from point sources along the shorelines. Once harvested for food, these eels became too contaminated to eat. In the early 2000s, about 500 beluga whales feeding on eels in the St. Lawrence estuary became contaminated with polychlorinated biphenyls (PCBs) and Mirex, an insecticide banned since the 1970s. These toxins still linger in lake sediments, which the eels disturb while feeding. The American eel in Lake Ontario was classified as endangered in 2008.

Human Impact

The Erie Canal was opened in 1825, and served as a major pathway for species from the Atlantic Ocean and Hudson River to the Great Lakes. The opening of the Welland Canal in 1829 provided a passage around Niagara Falls for other invaders. With the opening of the St. Lawrence Seaway in 1959, there was an increase in ship travel into the Great Lakes. Ships emptied ballast water containing animals such as the quagga mussel and the spiny waterflea into the lakes, resulting in serious damage to the Great Lakes ecosystems.

In 1988, zebra mussels were inadvertently introduced to Lake St. Clair, and they quickly spread throughout the Great Lakes region following flooding in the Mississippi River drainage in 1993. They mature much more quickly than native mussels and reproduce at a rapid rate. They have caused severe problems at power plants and municipal water supplies, clogging intake screens, pipes, and cooling systems. These filter feeders compete with native clams and mussels, and have nearly eliminated the native clam population in the Great Lakes ecosystem. Mussel tissues are heavily contaminated with PCBs, and these toxins, among others, are excreted in their fecal pellets, which form part of the lake-bottom sediment. Bottom-feeding animals then help pass the toxins up the food chain, eventually to the salmon and other top predators, including humans.

Other invaders in Lake Ontario include the spiny waterflea (a competitor and predator of native zooplankton), the fish hook waterflea, the round goby (which eats the eggs of native fishes), and the sea lamprey (a parasitic fish that preys on large fish such as salmon). Aquatic ecologists have determined that the numbers of a tiny crustacean called Diporeia are decreasing. Diporeia formerly represented up to 70 percent of the bottom-dwelling invertebrates and was food for bottom-feeding fish such as smelt and slimy sculpins, which, in turn, were eaten by salmon and trout.

Pollution has historically been a problem for Lake Ontario, resulting in frequent toxic algae blooms in the 1960s and 1970s. Cleanup efforts temporarily improved water quality, but continued pollution caused algal blooms to remain an occasional issue. In an effort to prevent these, New York State imposed limits on the percentage of phosphorus in fertilizers and dish detergents in 2010. This type of pollution endangers the drinking water of over nine million people, including 25 percent of Canada's population which lives within Lake Ontario's watershed. However, in the late 2010s, the coastal population began decreasing, and by 2022, the average coastal population around Lake Ontario reached a historic low.

Because of the lake’s size and the human population it supports, some environmentalists consider it the most vulnerable and threatened Great Lake. Climate change in the Great Lakes region has caused lower water levels, warmer air and water temperatures, less winter ice cover, and more extreme storms. With a shorter ice cover season, there is a higher potential for evaporation. Lake Ontario’s water helps moderate the local climate, and as climate change alters the lake's water, local weather will be transformed, impacting local economies and communities. The health of the biome and its components will be further compromised: the plants, birds, fish, and intangible benefits derived from the ecoregion. There are limits to adaptation, and when wildlife cannot adapt, there is a loss of diversity and shifting of species.

Conservation efforts in the region in the twenty-first century are abundant. To protect a vulnerable and ecologically important southeastern portion of the lake, the National Oceanic and Atmospheric Administration (NOAA) created the Lake Ontario National Marine Sanctuary in 2024. This designation created an advisory council to develop a management plan to effectively address threats to the lake, ensure a safe habitat for threatened or endangered species, and increase research, community engagement, tourism, and education opportunities.

Bibliography

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