Different environments can be affected by various types of pollution. how would bacteria and algae in a pond kill fish and other aquatic wildlife?

By using the majority of oxygen present in the water.

Explanation:

Bacteria and algae present in a pond would probably kill fish and other wild aquatic species as they can utilize the majority of the oxygen present in the water body. Fish and other species found in such waters surely would require more oxygen in order to thrive.  

Thus, if algae and bacteria would consume the majority of the oxygen found in water, then naturally the species present in the water would be not able to survive the loss of that very essential constituent.