Answer: increased oxygen levels.
Step-by-step 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.