- Farmers spray fertiliser on fields
- Fertiliser contains ammonium ions and nitrate ions, which help crops grow
- When it rains, fertiliser dissolves water
- Fertiliser enters rivers through a process called leaching
- Fertiliser makes algae in rivers grow quickly (algal bloom)
- Algae grow more quickly and block the light
- Pond plants die due to lack of light, which should be used for photosynthesis
- Bacteria in water decay dead plants
- Bacteria use up the oxygen during aerobic respiration
- Fish die from lack of oxygen - diminishing all life from the river
