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Humans and Freshwater Ecosystems

Boat on a lake at sunset

Boat on a lake at sunset (Elenathewise, iStockphoto)

Boat on a lake at sunset

Boat on a lake at sunset (Elenathewise, iStockphoto)

Let's Talk Science

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Learn about how people impact the ecosystems of lakes and rivers.

Freshwater ecosystems play an important role in Canada. 

In the past, people used rivers and lakes for travel. They also used them to trade furs, harvest fish and transport logs. Rivers are still an important way to move things to international markets. They are also a source of hydroelectricity

Historical illustration of Des Chats Falls on the Ottawa River
Des Chats Falls. Currier & Ives lithograph c.1900 (Source: United States Library of Congress's Prints and Photographs division under the digital ID pga.08656. Via Wikimedia Commons).


Lakes and ponds can also help to reduce flooding in towns and cities. A flood is when excess water covers land that is usually dry. Flooding can be a problem in places where there are a lot of roads and buildings. This is because water can’t pass through these things. It goes over or around them instead. 

Rivers and ponds can also bring wildlife into urban places that don’t have many parks or green spaces. And scientists have proven that being close to nature can improve your well-being

Deer Lake near Burnaby BC
Deer Lake Park in the city of Burnaby, British Columbia (Source: Alex_533 via iStockphoto).


Plants living in bodies of water can collect carbon from the atmosphere. The term for this process is carbon sequestration. Plants take in carbon dioxide from the air. Then they use it to make the sugars they need for energy in a process called photosynthesis. When the plants die, they sink to the bottom of the water. This deposits the carbon they absorbed. Carbon sequestration is how ponds reduce greenhouse gases that contribute to climate change.

Many people use lakes and rivers for boating, swimming and fishing. Tourists come from around the world to enjoy them as well.

In the past, people often thought wetlands were useless land. People caused many direct impacts on wetlands. These include dredging wetlands to create harbours for ships and draining wetlands to build farms and cities.

Humans have also caused indirect impacts on wetlands. This includes the introduction of invasive species. These are plants and animals that are not native to the area. Invasive species can outcompete native species. This sudden change can have a negative effect. It can harm other species in the food web and the wetland ecosystem.

Scientists now have a better understanding of wetlands. They know they are important water reserves. Most of the water we use every day comes from water stored underneath wetlands. They know wetlands also act as filters. They remove suspended particlesfertilizers and toxic pollutants from the water. They know that wetlands can act like giant sponges during floods. They can absorb extra water. Finally, wetlands are a unique ecosystem. They supply food and spawning areas for many types of animals

Water quality is the chemical content, physical characteristics and biological nature of water. It can include many measurements. Temperature is one. Concentration of substances, like dissolved oxygen or heavy metals, is another. And the number and kinds of microorganisms is another. Water quality can change for many reasons. Some changes are natural and human activities cause others.

Water from rain and melted snow runs across the land towards lakes and rivers. This term for this water is surface runoff.

Surface runoff can pick up many things along the way. Runoff in cities and towns picks up litter and organic matter from the streets. It can also pick up things like salt, sand, gasoline and motor oil and carry them into storm drains. And all these materials end up in aquatic ecosystems.

debris at street drain
Litter and other debris at a street runoff drain (Source: carlosrojas20 via iStockphoto).


Surface runoff can also contain things like herbicides, pesticides and fertilizers. People use these chemicals on lawns, gardens and golf courses. Herbicides kill unwanted plants and pesticides kill unwanted animals. These chemicals are as harmful in water as they are on land. 

Fertilizers have nutrients that plants need. These include phosphates and nitrates. When fertilizers get into a body of water, they can cause algae there to grow quickly. When these algae die, microorganisms break them down. Microorganisms use oxygen to do this. This means there is less oxygen in the water. Low oxygen levels can lead to fish and invertebrates dying. This term for this process is eutrophication

Laundry detergents often contain phosphates. These make detergents work better, but they can get washed into aquatic ecosystems. This also causes eutrophication.

Fertilizer spreader
Applying fertilizer pellets on a lawn (Source: BanksPhotos via iStockphoto). Farming, mining and industrial activities also affect water quality. 

Farming, mining and industrial activities also affect water quality. 


Runoff from farmland can contain pesticides, fertilizers and animal waste. It can also have small rock particles. These are from the erosion of soil in farm fields. Animal waste can have fecal coliforms. These are bacteria and other harmful microorganisms.


There are four main ways mining affects water quality.

  1. Acid Mine DrainageThis happens when rocks with sulphide minerals react with water and oxygen. This produces sulphuric acid. Surface runoff takes this acidic water from mines into rivers and lakes. This can change the acidity, or pH, of the water.
  2. Heavy Metal Pollution. This happens when mined rock containing metals comes into contact with water. These metals could include arsenic, cobalt, copper, cadmium, lead, silver and zinc. Surface runoff can carry these metals into bodies of water.
  3. Processing Chemicals Pollution. This happens when chemicals spill or leak into nearby bodies of water. These chemicals can be toxic to people and wildlife.
  4. Erosion and Deposition. Mining can cause the erosion of large amounts of rock and soil. Eroded materials can block the flow of water when in rivers and streams.
water pollution near mine
Aerial view of mining industry near Sechelt Inlet, British Columbia. Note the colour of the water in the water by the mine versus the water in the river (Source: edb3_16 via iStockphoto).


Industrial Activities

Industrial waste is waste made by manufacturing and other industries. It includes things like garbage, scrap metal, gravel, grass clippings and chemicals. Industrial waste can be solid or liquid. Liquid waste like cleaning fluids, paints, dyes and solvents contributes to water pollution. Sometimes this waste is pumped into lakes and rivers. Sometimes it leaks out of storage containers. Industrial waste can harm aquatic ecosystems. It can make water unusable, now or in the future. 

Many living things depend on lentic ecosystems and lotic ecosystems. Many people recognize the value of lakes, rivers and wetlands. Governments are writing laws and regulations to protect freshwater habitats. We are also making efforts to restore and preserve these ecosystems. 

Conservation includes rehabilitating or restoring areas to health. It also includes purchasing or securing land with important habitats. Rehabilitation can include re-establishing natural water levels. It can also include controlling invasive species and removing contaminated sediments.

Here are some things you may be able to do to keep these ecosystems healthy. These steps will help improve water quality and the environment.

  • Don’t rinse bits of food down the drain. Compost them instead. 
  • Don’t flush garbage down the toilet. Put it in the garbage can.
  • Use cleaning products that are low in phosphorus. These can cause less eutrophication.
  • Don’t use chemical herbicides or pesticides. Pick weeds by hand.
  • Don’t pour paints or chemicals down the drain. Bring them to a liquid waste collection centre. 
  • If you’re out on a boat, don’t throw garbage overboard. Keep it until you get to shore and dispose of it properly. 

Many organizations are working to conserve Canada’s aquatic ecosystems. One way you could help is through a local shoreline clean up. Or you could contact local environmental groups for other ideas.


The Dirt on Soil Conservation (2020)

Learn about how soil plays a very important role in supporting all life on Earth in this article from Let’s Talk Science. 

Crack the Code: Water Systems 

Try this Google site escape room-type game by Let’s Talk Science.


The Canadian Atlas Online. (n. d.). Water Pollution.

Earth Networks. (n. d.). Flood Causes and Effects

Government of Canada. (2020, January 24). Agriculture and water quality - Agriculture and Agri-Food Canada (AAFC).

Ontario Ministry of Natural Resources and Forestry. (2017). A wetland conservation strategy for Ontario 2017-2030. 

Oram, B. (n. d.). Water Testing Fecal Bacteria Pathogenic Organisms Water. Water Research Center.

Safe Drinking Water Foundation. (n. d.). Industrial Waste.

Safe Drinking Water Foundation. (n. d.) Mining and Water Pollution

USGS. (n. d.). Mining and Water Quality

World Wildlife Fund. (n. d.) Canada’s Watershed Report.