Answer: The decrease in oxygen levels was also caused by the increased algal growth.
Step-by-step explanation:
The solubility of the oxygen in the water will decrease when the temperature of the water increases. The decrease in oxygen levels in water can also be because of increase in algal growth in water. The algal growth occurs over the surface of the water body, this restricts the dissolution of atmospheric oxygen to the water body. This deteriorates the quality of the water and makes the water body unfit for the survival of the animals in it. This process is called as eutrophication.
On the basis of the above explanation, The decrease in oxygen levels was also caused by the increased algal growth. can be the additional explanation which is most likely correct.