Plant like organism generate very much oxygen that kills the fishes in last few years.
Eutrophication:
It is process in which algae grow too much in the water body that it cover the whole surface due to the presence of high nitrogen and phosphorus content in the water.
It can be caused by,
- Over use of nitrogen and phosphorus fertilizers near the water body.
- The organic pollutants such as gutter waste.
Therefore, plant like organism generate very much oxygen that kills the fishes in last few years.
To know more about Eutrophication,
https://brainly.com/question/13232104