What happens to animals if the water is polluted?

That is a very good question. So I'll answer it. Let's say that in 50 years, all of Earth's lakes, oceans, and rivers will be dangerously polluted. Then, all the fish in the bodys of water will die and so will the marine plants and sea animals. The next thing that could happen would be that the oxygen in the water and possibly the air will be gone, letting plants, animals, and even us Humans die of sufucation from the lack of oxygen and the rise of deadly, toxic fumes. Are you following me here?