All of the following are possible outcomes if waterways continue to be polluted except

increased oxygen levels.
reduced fish respiration and plant productivity.
increased amounts of bacteria and protozoans.
increased growth of aquatic plants and algae.

increased oxygen levels.

Explanation:

The waterways is the part of the water body which is used for the purpose of water transportation. The waterways can be polluted by the oil spill, biological means by the excess growth of bacteria, aquatic plants and algae. These will limit the oxygen content of the water body. The water density will increase due to increase in population of these organisms these will also deteriorate the quality of water.

Therefore, on the basis of the above explanation, increased oxygen levels is the correct option because it is not the possible outcome if the waterways continue to be polluted. As the increase in abundance of oxygen is likely to improve the quality of water.

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.