Eutrophication
Explanation: It is known that some aquatic life are poorly fed due to absence or low production of organic matter by photosynthesis. Some waters are poorly fed due to lack of certain important elements like nitrogen and phosphorus and this has cause the death of some aquatic life especially those from oligrotrophic water source.
Eutrophication is one of the benefit that we receive as human to provide the aquatic life with necessary nutrient and organic matter resulting in high biological productivity.