Final answer:
Excessive phosphorus in surface water leads to eutrophication, causing algal blooms and subsequent oxygen depletion, which results in death of aquatic life and formation of 'dead zones' in affected bodies of water.
Step-by-step explanation:
Excessive phosphorus in surface water has been linked to a condition known as eutrophication. This process starts when excess phosphorus and nitrogen, largely from fertilizers and sewage, enter aquatic ecosystems. The increased nutrient levels cause algal blooms, which are rapid increases in the population of algae. When these algae die, their decomposition consumes a significant amount of the dissolved oxygen in the water, leading to oxygen depletion. This depletion can cause the death of aquatic organisms, such as fish and shellfish, and creates areas known as 'dead zones' where aquatic life cannot survive due to the lack of oxygen. These dead zones are observed in various lakes and at the mouths of major rivers around the world, often resulting in massive fish kills, particularly during the summer months.