What is eutrophication ?
Originally, eutrophication is a step of the natural process which tranforms slowly a shallow lake in a marsh and then in a meadow and finally in a forest. This filling come from the lake aging process which is natural with a nutrients and sediment input due to the erosion and the water run-off.
This phenomenon can be speed up by human activities in a few years instead of hundreds or thousands years.
Nowadays, eutrophication is used to talk about the evolution of the aquatic environment trophic status (produced organic matter according to phospohorus and nitrogen inputs).
Finally, eutrofication will cause the decrease of the water bodie biodiversity. The algae development increase will cause the light decrease at the bottom and so the photosynthesis phenomenon will stop.