Our water at risk
Clean water is essential for drinking, farming, industry and wildlife. Water pollution happens when harmful substances get into lakes, rivers, oceans or groundwater, making them unsafe.
Where water pollution comes from
| Type | Description | Examples |
|---|---|---|
| Point source pollution | Comes from one identifiable place | A factory discharge pipe, a sewage treatment plant, an oil spill from a ship |
| Non-point source pollution | Comes from many scattered places; hard to trace | Runoff from farms, lawns, streets and parking lots |
Non-point source pollution is now the biggest cause of water pollution in many places, because it’s so hard to control.
Types of water pollutants
| Pollutant | Sources | Effects |
|---|---|---|
| Sewage | Toilets, overflowing sewers | Spreads disease; uses up oxygen |
| Nutrients (nitrogen and phosphorus) | Fertilizers, manure, detergents | Algal blooms, dead zones |
| Toxic chemicals | Factories, mines, pesticides | Poison fish and wildlife; health risks for people |
| Heavy metals (mercury, lead) | Mining, industry, old pipes, coal burning | Build up in food chains; damage brains and nerves |
| Oil | Spills, leaks, road runoff | Coats birds and animals; kills marine life |
| Plastics and microplastics | Litter, synthetic clothing, tire wear | Animals eat or get tangled in them; enter food chains |
| Sediment | Construction, erosion, logging | Clouds water; smothers fish eggs |
| Heat (thermal pollution) | Power plant cooling water | Warm water holds less oxygen |
| Road salt | Winter de-icing | Harms freshwater life |
Eutrophication
Eutrophication happens when too many nutrients, mostly from fertilizers and sewage, enter a lake or coastal area.
- Nutrients feed huge growths of algae (algal blooms).
- Algae cover the surface, blocking sunlight from plants below.
- When algae die, bacteria decompose them, using up oxygen in the water.
- Fish and other animals suffocate, creating "dead zones."
Some blooms of blue-green algae (cyanobacteria) also release toxins that make water unsafe to drink or swim in.
Lake Erie and Lake Winnipeg have both had major algal blooms. In 2014, a bloom in Lake Erie made the water in Toledo, Ohio, unsafe to drink for days.
Biomagnification
Some pollutants, like mercury and certain pesticides, don’t break down. They build up in living things and become more concentrated at each level of the food chain.
plankton → small fish → large fish → seals or people
This is called biomagnification. It’s why health agencies advise limiting how much of certain large predatory fish, like some tuna and swordfish, people eat.
Water pollution in Canada
| Event or issue | Details |
|---|---|
| Walkerton, Ontario (2000) | E. coli from farm runoff contaminated the town’s water; seven people died and thousands became sick. This led to stronger drinking water laws. |
| Drinking water advisories | Many First Nations communities have faced long-term advisories; work continues to lift them |
| Great Lakes cleanup | Canada and the U.S. have cooperated since 1972 under the Great Lakes Water Quality Agreement |
| Oil spills | Pipeline and tanker risks on coasts and rivers |
| Mining | Tailings ponds can leak toxic substances |
Cleaning water
Wastewater treatment cleans sewage before it returns to rivers and lakes.
| Stage | What happens |
|---|---|
| Primary | Screens and settling tanks remove solids |
| Secondary | Bacteria break down organic matter |
| Tertiary | Extra filtering and chemicals remove nutrients; disinfection kills germs |
Drinking water treatment filters and disinfects water before it reaches your tap.
What you can do
- Never pour paint, oil, medicines or chemicals down drains or storm sewers. Storm drains often lead straight to lakes and rivers.
- Use less fertilizer and pesticide, or none, on lawns.
- Pick up pet waste and litter.
- Wash cars at car washes that treat their water.
- Choose natural fibres or use laundry filters to reduce microfibres.
- Join a shoreline cleanup.
Common mistakes
- Thinking storm drains go to treatment plants. Many go directly to waterways.
- Thinking clear water is clean water. Many pollutants are invisible.
- Thinking only factories pollute water. Everyday runoff from homes and farms is a major source.
Try it yourself
- Make a model watershed with crumpled paper covered in plastic. Sprinkle "pollutants" (cocoa powder for soil, coloured sugar for fertilizer) and spray with "rain." Where does it end up?
- Build a simple water filter from sand, gravel and charcoal in a cut plastic bottle. Filter muddy water (don’t drink it!).
- Find out where your community’s wastewater goes after it leaves your home.
Quick recap
- Water pollution comes from point sources and non-point sources like runoff.
- Pollutants include sewage, nutrients, chemicals, metals, oil, plastics and sediment.
- Eutrophication causes algal blooms and dead zones.
- Some pollutants biomagnify up food chains.
- Treatment plants and careful everyday choices help protect water.