# Describe the effects of eutrophication on the organisms living in a lake.

> Eduqas A-Level Biology — 3.6 Human impact on the environment · Describe · 5 marks

> Farmers sometimes apply fertilisers to their fields. Rain can wash nitrates and phosphates from the soil into nearby lakes, causing eutrophication.

## Mark scheme (5 marks)

1. Nitrates/phosphates cause rapid growth of algae (algal bloom)
2. Algae block light from reaching plants below the water surface
3. Submerged plants die because they cannot photosynthesise
4. Decomposing bacteria break down the dead organisms and use up oxygen
5. Fish and other aquatic animals die due to lack of oxygen

## Key terms

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

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-the-effects-of-eutrophication-on-49751e69) · Published by Druglandscape Ltd.