There are four main causes of pollution:
1. Agriculture - Farmers put fertilizers + pesticides on their crops so that their crops grow better. But these fertilizers and pesticides can be washed through the soil by rain, to end up in rivers.
2. Factories - Factories use water from rivers to power machinery or to cool down machinery. Dirty water containing chemicals is put back in the river. Water used for cooling is warmer than the river itself, and this is also a form of pollution.
3. Mines - Waste water from old tin, coal and lead mines is a problem. When the mines were in use, they had pumps to keep them dry. Now, water drips through the old mine shafts + fills tunnels. The water reaches the surface by springs after coming into contact with rusty machinery.
4. People - People are sometimes careless and throw rubbish such as bottles + crisp packets directly into rivers.
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