What is eutrophication? Explain how this process can cause harm to the environment, particularly when farmers apply fertiliser to their land.

Eutrophication describes a process wherein a substance containing excessive levels of nutrients, in this case fertiliser, is applied to land and leaches off into nearby bodies of water (often as a result of rainfall). This causes a large amount of plant growth and algal bloom in the water; the overcrowding of these plants causes those beneath the top layer to die as they cannot perform the process of photosynthesis due to the blocking of light and the general lacking of resources available. When these plants die, bacteria acts on them, causing them to decay and, in doing so, use up the oxygen in the water for respiration. These hypoxic conditions prevent the fish present from respiring, resulting in their death.