Explain the process of eutrophication.

Leaching from the excessive use of fertilisers causes a nutrient build up in neighbouring rivers or lakes. As a result of the increased nutrients plants within the lake or river grow rapidly, including algae on the surface of the water. The growth of algae is called an algal bloom, when this occurs it prevents sunlight from getting through the surface and down to the plantlife on the riverbed, as a result they die. The death of this plantlife results in reduced oxygen in the water, and the plant matter is broken down by decomposer bacteria which use up any remaining oxygen within the water. As a result of the lack of oxygen in the water any animal life - fish and other organisms - die.