A lot of modern farming involves the use of chemical fertilisers, insecticides and herbicides. The yields that farmers have been able to produce have grown enormously. However, these chemicals continue to work after they have been washed off the land into rivers and the water supply. This has led to changes in the flora and fauna of intensively farmed areas. River estuaries have suffered from the growth of weed and algae, as the levels of nitrates in the water has increased.

Governments have tackled this problem by careful monitoring of pollution levels, with fines for the worst offenders. Some farmers have chosen to go "organic", which means they do not rely on artificial chemicals. As well as having environmental benefits the farmer can charge more for the produce as the consumer is willing to pay extra for organic goods.