From the graph we see that the fish population continue to decrease with time. As time passed on, the fish population keeps suffering a decline. In retrospect, the population of the algae continued to increase.
We can ascribe this to the pond experiencing an algae bloom.
It could be due to condition called eutrophication.
When nutrients become very much in water and more algae is produced.
This leads to dissolve oxygen amount reducing in the water body.
