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Our Great Lakes

We all have a stake


Our Great Lakes

Great Lakes pollution has been problematic for decades. We look at the health of this ecosystem today and the issues that will affect its health in the future.

If you live in Ontario, you very likely live within the Great Lakes watershed. Even if you don’t live close to the water, what you do—and what everyone around you does, including individuals, governments, and industry—affects the water in the lakes and the ecosystems they support.

But even if you don’t live in Ontario, you also have a stake in the health and viability of the Great Lakes. After all, this water system—the largest on earth—affects our way of life as well as all aspects of the natural environment, from weather and climate to wildlife and habitat.

The state of the Great Lakes affects many facets of daily life: the quality of local drinking water, recreation, availability of food, and the ability to support industry.

On the other hand, the health of the Great Lakes ecosystem is directly affected by many challenges: invasive species, shoreline development and urban sprawl, destruction or loss of habitat, climate change, and pollution.

Invasive species

More than 140 exotic aquatic organisms (including plants, fish, algae, and molluscs) have become established in the Great Lakes since the 1800s. Invasive species—species that are non-native to the area and negatively impact the health of the ecosystem—play a huge role in the changing ecosystem of the Great Lakes.

Sea lamprey
The invasion began before the opening of the St. Lawrence Seaway, says Fabio Tonto, water program manager at Pollution Probe, a Canadian environmental organization.

With the opening of the Erie Canal linking Lake Ontario with the Atlantic Ocean in 1825, sea lamprey, a non-native, parasitic jawless fish, entered the Great Lakes system. Because they did not evolve alongside the native fish in the Great Lakes, they were easily able to outcompete their prey.

Preying on all large lake fish, the lamprey played a substantial role in the decline of species such as lake trout during the 1940s and 1950s. Since that time, control measures have reduced the presence of this invader by 90 percent, but control efforts must continue to keep this species in check.

Zebra mussel
Since its discovery in the Great Lakes in 1988, the zebra mussel has become a threat to native species of mussels as well as Great Lake fish. An efficient filter feeder, the zebra mussel reduces local food sources for the native mussels and fish.

The zebra mussel has caused the decline of zooplankton in Lake Huron and Lake Michigan, as well as the decline of Diporeia (a native bottom-dwelling invertebrate) in Lake Huron, Lake Michigan, and Lake Ontario, and possible extinction in some areas of Lake Erie.
Zooplankton and Diporeia are important sources of food for many aquatic species in the Great Lakes, and their decline impacts the whole food web.

Asian carp
DNA from the invasive species of Asian carp that has devastated the Mississippi River ecosystem has been found in Lake Michigan. The carp, which can grow up to 100 pounds (45 kg) and consume 20 percent of its body weight in plankton daily, has scientists concerned because it is very well adapted to this environment and could outcompete the native species.

An electronic barrier has been placed in the Mississippi River at Chicago to prevent the invasive species from reaching the Great Lakes system. Although Asian carp DNA has been found in some water samples beyond the barrier, no actual carp have been spotted in the lake at this time.

Urban growth and development

Urban sprawl is placing greater demands on existing infrastructure (such as sewage systems) and on water supplies. Rural areas once had healthier environments than their urban counterparts, but now we are seeing an increase in pollutants in rural areas, too.

Although more efficient industrial use has shown a decrease in water consumption in the US and Canada since 1980, population growth will continue to place greater demands on our water supply.

The quality of treated drinking water remains good, but in order to ensure this quality in the future, we must improve and protect the water at its source.

Shorelines and wetlands
Not only are the shorelines, wetlands, and islands of the Great Lakes basin important habitats for migratory and nesting birds, as well as flora and fauna, but they also affect the aquatic habitat of the Great Lakes.

Shorelines and wetlands act as natural filters of pollutants and are home to many species of plants and animals, some of which are rare or endangered species. Urban development reduces the habitat for these species and also acts as a conduit for invasive species.

A major concern involving shorelines and wetlands of the Great Lakes basin, called artificial hardening, is caused by pavement and urban development and involves alteration of the lakes’ natural cycles of deposition and erosion by man-made structures.

Hard shorelines increase runoff and pollutants from our sewers and waste systems into the lakes. The highest incidences of shoreline hardening occur along the Detroit, Niagara, and St. Clair rivers, with Lake Erie having the highest percentage of shoreline hardening.

Water levels and climate change

Naturally fluctuating water levels in the Great Lakes are crucial to maintaining a healthy ecosystem. Plant and animal life adapts to these cycles, and the ecosystem is more productive than if lake levels had remained consistent.

In 2000, however, water levels in the Great Lakes were recorded to be lower than the 140-year average. We are not yet sure if this is part of the historic norm or the effects of climate change.

To be sure, the climate of the Great Lakes basin is changing. Precipitation and temperature patterns are less predictable, and extreme weather conditions are occurring more frequently. Annual temperatures are warmer, with shorter winters and hotter summers.

Scientists are creating GCMs (general circulation models) to try to predict future climates. “These aren’t the lakes that were around 20 years ago. We’re still basically catching up and doing the science to learn what kind of environment we are dealing with now,” explained Tonto, of Pollution Probe.

Scientists fear that, due to climate change and warmer annual temperatures, the evaporation of water will increase. Warmer summers and reduced ice cover during the winter could allow this to happen.

Since 99 percent of the water in the Great Lakes is from ancient glacial melt water, once the water is gone, it can’t be replenished. Evaporation will also affect water quality and snowpack conditions.


Point-source pollution
Over the last 30 years there has been a decrease in point-source pollution (pollution that can be attributed to a specific industry, chemical, or company) due to the government’s recognition of the need to regulate emissions into the Great Lakes. The creation of bi-national legislation such as the Great Lakes Water Quality Agreement (GLWQA) has been a key player in the cleanup.

Good news

Bad news

  • contaminants found offshore are low and decreasing
  • mercury levels are well below criteria for drinking in offshore areas
  • decrease in PCBs overall
  • organochlorine pesticides, dioxins, and furans banned
  • DDTs have declined, but still higher than GLWQA criteria in most areas
  • PBDEs (flame-retardant chemical) increasing
  • mercury levels in harbours and near urban areas are above criteria for wildlife protection
  • re-suspension of contaminated sediments due to runoff and atmospheric deposition
  • concentrations of fossil fuel emissions (PAHs) are greater in lower Lakes due to greater usage
  • PFOs (perfluorooctane sulphonate) from water repellents and fire-suppressant foams have been detected in fish throughout the Great Lakes

The Great Lakes’ vital stats

  • There are five Great Lakes: Superior, Huron, Erie, Ontario, and Michigan.
  • Combined, these lakes make up approximately 20 percent of the world’s fresh water supply.
  • Less than 1 percent of the Great Lakes water is replenished annually from precipitation. The rest of the water in the Great lakes “is a historic gift” that came from glacial melt waters.
  • The Great Lakes basin is approximately 766,000 square kilometres (that’s bigger than Texas!) and is home to one-third of Canada’s population.
  • The lakes and basin play a significant role in tourism, recreation, and our economy.
  • Within the Great Lakes system is the world’s largest collection of freshwater islands. Some of these islands contain rare or endangered species of wildlife. The lakes themselves are home to an array of aquatic life and many fisheries.

Nonpoint-source pollution
Land runoff pollution—or nonpoint-source pollution—is increasing due to agricultural use in the basin, which results in nutrient runoff into the lakes. The runoff increases nutrient levels—phosphorus, for example—in the water systems, which in turn results in harmful algal blooms that create oxygen levels too low for most aquatic life to survive.

These “dead zones” are a direct result of human intervention, with agricultural runoff, urban storm water runoff, and sewage being the major causes. Though Lake Erie bounced back after being declared dead from phosphorus pollution, the phosphorus levels are once again increasing.

Combined with the effects from the invasion of the zebra mussel, the algae Cladophora has reappeared along the Lake Erie shoreline, resulting in decreased water clarity and quality. Dead zones are appearing in the Western Basin and expanding in the Central Basin.

As well, pharmaceuticals and personal care products are being introduced into waste water. Since the concentrations are low, it would be very expensive for them to be removed at the water treatment plants, but over time these low concentrations accumulate in the lakes, resulting in recognizable concentrations.

Beach advisories
Pollution from all sources affects recreational use of the lakes. There are generally more beach advisories posted around Lake Ontario and Lake Erie due to the greater number of point- and nonpoint-pollution sources.

On average, 67 percent of Great Lakes beaches in the US and Canada were open 95 percent of the swimming season (based on 2007 data).

Air pollution
There is some good news on the air pollution front: we are seeing an overall reduction in air pollution in the basin. There has also been a decrease in nitrogen oxides in both Canada and the US due to improvements in urban areas.

The Great Lakes basin supports

  • nearly 40 percent of our gross domestic product
  • 25 percent of our agricultural production
  • over 50 percent of our manufacturing industry


State of the lakes

Lake Superior


  • overall ecosystem in
    good condition
  • species such as the bald
    eagle, grey wolf, and peregrine falcon are recovering
  • lower food web stable; fisheries in good to excellent condition
  • forest cover increasing


  • stressors include: climate change, invasive species, loss of habitat, and shoreline hardening and mining
  • toxic chemicals and fish consumption advisories
Lake Huron


  • partnerships developing to protect diverse habitat
  • working on restoration of recreational-quality lake and beaches


  • major changes to the food web
  • effects of algae reducing water quality
  • new diseases
Lake Ontario


  • continued reduction of contaminants
  • bald eagle nesting territories increasing and a strong bird population


  • predatory zooplankton and zebra mussels outcompeting natural species; may impact the food web
  • near-shore algal blooms create beach closures, water quality concerns, and costs to industry
Lake Erie


  • nutrient management top concern for improving lake
  • yellow perch stocks recovering


  • species such as lake trout and walleye still struggling
  • PCBs and mercury still affect fish consumption
  • aquatic invasive species are changing the food web and may influence near-shore algal growth and botulism
Lake Michigan


  • good source of treated drinking water
  • reduction in beach advisories
  • rebound of wildlife and aquatic species due to habitat restoration and dam removal
  • decline in fish contaminants


  • water levels below average
  • invasive quagga mussel dominates; interaction with nutrients leads to algal growth
  • food web disruptions including the disappearance of Diporeia, an important bottom-feeding invertebrate
  • septicemia found in fish

Water power resources

  • Statistics for 2004 show that 164 L of water were withdrawn from the Great Lakes basin daily—83 percent for thermoelectric and industrial use and 14 percent for public water system use.
  • The water return rate was 95 percent, with a 5 percent loss attributed to consumption.
  • Due to the closure of nuclear plants and increased efficiency of thermal plants, water use has decreased since 1980.
  • Studies are underway to examine the potential of wind power projects in the Great Lakes region.

People of the Great Lakes

  • Canada’s Great Lakes basin population increased 16.3 percent between 1996 and 2006 to over 8 million.
  • The US Great Lakes basin population grew 7.6 percent between 1990 and 2000 to over 28 million.
  • Approximately 5 million people fish in the Great Lakes.
  • One million boats operate on the lakes (mainly pleasure crafts).

What does all this mean?

Something that we have to keep in mind is that the Great Lakes are no longer a natural ecosystem; they are a managed ecosystem. Their future depends on how well we manage them.
Though largely misunderstood and mistreated in the past, the fragile ecosystem that this great water system supports is showing the positive signs of greater understanding and respect.

Within the next year the GLWQA will be renegotiated. Many of the lakes’ improvements are the results of past versions of this agreement. Pollution Probe’s Tonto says, “Essentially it [the] can be a very good news story, but it’s all about what the two governments negotiate.

“If they negotiate ambitious goals that will really value the lakes for what they create in this part of the world it could be an amazing story; it can be something really positive. If, on the other hand, they’re not motivated to do so, then it’s an opportunity lost.”

Species regeneration

  • Lake trout have rebounded in Lake Superior and no longer have to be stocked.
  • Walleye populations have increased in the Great Lakes, although harvests are still below target levels.
  • Bald eagle populations have also rebounded in the Great lakes region.

What can I do to help?

If you live in the Great Lakes watershed, there are many things you can do to help protect this valuable ecosystem.

Dispose of hazardous materials properly
Our water treatment facilities are designed to handle waste water and not chemicals. Household chemicals, pesticides, and pharmaceuticals can pass through the treatment plants and into the lakes, harming aquatic life and the quality of our drinking water. Choosing green detergents, soaps, and personal products will also reduce harm to this precious ecosystem.

Stop invasive species
Invasive species may be small and travel on boat hulls, trailers, or water stored in motors and on the boat. Clean your boat and accessories on land far from open water. Bait and aquarium fish may not be native to your area, so don’t dump them into the lakes or their tributaries.

Conserve water
Each person uses about 90 gallons (340 L) of water a day—65 percent is used in showers, baths, and flushing the toilet. Install low-flush toilets and low-flow faucets. In summer, keep lawn watering and car washing to a minimum.



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