Book 19, Question 39
Why Do Some Rivers Have Foam on Top?
Some rivers have foam on top, and often it is completely natural! Leaves and plants release soap-like substances into the water. When the water tumbles over rocks, it whips in air.
More fun facts
- Foam often forms naturally when decaying leaves, wood and other plant material mix into the water.
- These natural materials change the water so that bubbles form and last more easily.
- Churning, splashing water stirs air into water that is rich in plant material, and that forms the bubbles.
- Streams that start in wetlands, bogs or woods often have brown, tea colored water from tannin, which comes from rotting wood.
- Foam is common in dark streams in late fall and winter, when plants are breaking down in the water.
- On windy days, foam can collect in long lines along the shore or streak across open water.
- Some foam can be a sign of pollution, for example from factories, car washes, firefighting foam or construction mud.
Sources: michigan.gov
Questions kids ask
Should you touch river foam?
It is best not to. Most foam is natural, but some comes from pollution, so look but do not touch.