Name and explain the effect of fertiliser runoff into lakes

This process is called eutrophication. Fertiliser is applied to plants because it contains a lot of ammonia and nitrates, which are needed to help a plant grow. However, if too much is applied, especially in rainy weather, this can run into nearby lakes or rivers. This then causes algae, which often sits on lakes, to grow excessively and uncontrollably, covering the surface of the lake. This means that sunlight is unable to penetrate through and aquatic plant species cannot photosynthesis and produce oxygen in the water, leading to a depletion of oxygen levels in the water. Eventually the algae will die, and decomposing microorganisms will use up the remaining oxygen gas in the water during respiration as they break down the dead algae. Therefore oxygen levels in the water become so low that eventually this will lead to the death of fish and other aquatic species as they can no longer respire.