# Explain how the use of fertilisers on farmland can lead to the death of fish in nearby rivers.

> WJEC GCSE Biology (Wales) — 1.6.3 Human impact on the environment · Explain · 4 marks

> Farmers often apply fertilisers to their fields to increase crop yields. Heavy rainfall can wash these fertilisers into nearby rivers and lakes.

## Mark scheme (4 marks)

1. Fertilisers are washed into the river by rain (leaching/run-off)
2. Fertilisers cause algae/water plants to grow rapidly (algal bloom)
3. Algae block light, causing underwater plants to die
4. Bacteria decompose the dead plants/algae, using up oxygen, so fish suffocate/die

## Key terms

- [fertilisers](https://www.gradenine.co.uk/glossary/fertilisers)

## Related

- [Revision notes for WJEC GCSE Biology (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-use-of-fertilisers-3f3d402b) · Published by Druglandscape Ltd.