An example of an algal bloom that results from eutrophication © Johnnie Walker

Eutrophication is an environmental response to artificial nutrients and fertilisers being flushed into rivers and lakes. The excess nutrients or fertiliser cause plants and algae to grow rapidly. However, this vegetation bloom covers the water surface and prevents sunlight reaching deeper living plants. When plants die, they decompose and deplete oxygen levels in the water. Fish and other organisms die due to low oxygen levels and the ecosystem is severely degraded.