decrease in water temperature. reduction in oxygen levels. decrease in food supply. removal of minerals.
I gave my students this multiple choice question: The danger posed to fish in an aquarium by an overpopulation of bacteria caused by an algal bloom is most likely a

Only one answer is correct among these 4 choices:
- decrease in water temperature.
- reduction in oxygen levels.
- decrease in food supply.
- removal of minerals.

Could you tell me which one is correct?

reduction in oxygen levels.