Final answer:
Excessive phosphorus in surface water leads to increased algae growth (eutrophication), resulting in oxygen depletion and creating hypoxic conditions harmful to aquatic life.
Step-by-step explanation:
Excessive phosphorus in surface water has been linked to increased algae growth. This phenomenon, known as eutrophication, occurs when phosphorus, often from detergents, fertilizers, and sewage, becomes abundant in aquatic environments, promoting the rapid proliferation of algae. When these algae die, they become food for bacteria, which consume oxygen in the water to decay the algal mass, leading to oxygen depletion. This creates hypoxic conditions or 'dead zones' where aquatic life, such as fish and shellfish, cannot survive due to the lack of oxygen.