Pollution from sewage is one of the most serious forms of ocean contamination. It affects every region of the world. In Chile for example, it is estimated 82 percent of all domestic sewage finishes up in the sea, transported there by 27 river basins. Among seven regions that prioritized their marine problems from land-based activities, domestic sewage took top place in all of them.
Sewage can fertilize parts of the ocean to death. It brings phosphates and nitrates into the water and causes blooms of algae so prolific that the oxygen is depleted to the point where a 'dead' zone results