A precious resource
About 71% of Earth’s surface is covered in water, but nearly all of it is salty ocean water. Only about 2.5% is freshwater, and most of that is locked in glaciers and ice caps or deep underground. Less than 1% of Earth’s water is freshwater we can easily reach.
Where Earth’s freshwater is
| Location | Share of Earth’s freshwater |
|---|---|
| Glaciers and ice caps | About 69% |
| Groundwater | About 30% |
| Lakes, rivers, wetlands, soil moisture and the atmosphere | About 1% |
Canada’s freshwater
Canada is rich in freshwater:
- About 20% of the world’s freshwater is in Canada (though only about 7% of the renewable supply).
- Canada has more lakes than any other country, possibly over two million.
- The Great Lakes, shared with the U.S., hold about 20% of the world’s surface freshwater.
- Canada’s longest river, the Mackenzie, flows about 4200 km to the Arctic Ocean.
Freshwater ecosystems
Rivers and streams
Flowing water ecosystems. Fast mountain streams are cold and full of oxygen; slow lowland rivers are warmer and muddier.
| Section | Features | Life |
|---|---|---|
| Source (headwaters) | Cold, fast, clear | Trout, mayfly larvae |
| Middle | Wider, slower | Many fish, plants along banks |
| Mouth | Slow, muddy; meets a lake or ocean | Catfish, carp; deltas form |
Salmon hatch in rivers, swim to the ocean, then return to the same river to spawn.
Lakes and ponds
Still-water ecosystems.
| Zone | Description |
|---|---|
| Shoreline (littoral) zone | Shallow; plants rooted in the bottom; frogs, insects, turtles |
| Open water (limnetic) zone | Sunlit; plankton and fish |
| Deep (profundal) zone | Dark and cold; decomposers |
In summer, many Canadian lakes form layers: warm water on top and cold water below.
Wetlands
A wetland is land covered by shallow water for at least part of the year.
| Type | Features |
|---|---|
| Marsh | Grasses and cattails; common in the Prairies |
| Swamp | Trees and shrubs |
| Bog | Acidic, spongy peat moss; common in the boreal forest |
| Fen | Peat with flowing groundwater; less acidic than bogs |
Canada has about a quarter of the world’s wetlands. Wetlands filter pollutants, absorb floodwaters, store carbon and provide homes for ducks, frogs, beavers and many other species. They’ve been called "the kidneys of the landscape."
Groundwater and aquifers
Rain and melted snow soak into the ground and fill spaces between soil grains and cracks in rock. This is groundwater. An aquifer is a layer of rock or sediment that holds lots of groundwater. About 30% of Canadians, especially in rural areas, rely on groundwater from wells.
Watersheds
A watershed (or drainage basin) is all the land that drains into the same body of water. Whatever happens upstream affects everyone downstream. Most of Canada drains into Hudson Bay, a huge watershed covering about one-third of the country.
The water cycle
Freshwater is constantly renewed by the water cycle: water evaporates from oceans, condenses into clouds, falls as rain or snow, and flows through rivers, lakes and groundwater back to the sea.
Threats to freshwater
| Threat | Example |
|---|---|
| Water pollution | Sewage, fertilizer runoff, industrial chemicals, plastics |
| Algal blooms | Fertilizer runoff feeds algae in Lake Erie and Lake Winnipeg |
| Invasive species | Zebra mussels in the Great Lakes |
| Draining wetlands | Much of southern Canada’s wetlands have been drained for farms and cities |
| Overuse | Taking too much water from rivers and aquifers |
| Climate change | Shrinking glaciers that feed rivers; warmer lakes |
Many First Nations communities in Canada have lived under long-term drinking water advisories, meaning their water isn’t safe to drink without boiling or treatment. Governments and communities have been working to lift these advisories.
Protecting freshwater
- Don’t pour chemicals, paint or medicines down drains.
- Use less fertilizer on lawns.
- Pick up pet waste.
- Save water at home: take shorter showers and fix leaks.
- Join a shoreline or stream cleanup.
Common mistakes
- Thinking Earth has plenty of freshwater because it’s mostly water.
- Thinking groundwater is an underground lake. It fills tiny spaces in soil and rock.
- Thinking wetlands are useless swamps.
Try it yourself
- Use 100 drops of water to represent all of Earth’s water. Separate out the drops that represent freshwater (about 2.5) and easily accessible freshwater (less than 1).
- Find your local watershed on a map. Where does water from your home end up?
- Test water samples from a pond and tap water for clarity, smell and pH.
Quick recap
- Only about 2.5% of Earth’s water is fresh, and most is frozen or underground.
- Canada has a large share of the world’s freshwater and wetlands.
- Rivers, lakes and wetlands are freshwater ecosystems.
- Groundwater fills aquifers; watersheds connect land and water.
- Pollution, invasive species and climate change threaten freshwater.