The correct answer is D. Excessive entry of nutrient into water.
Eutrophication is a process by which a body of water becomes enriched in nutrients, particularly phosphorus and nitrogen. This can lead to excessive growth of algae, which can block sunlight and prevent other plants from growing. The algae can also die and decompose, which uses up oxygen in the water and can kill fish and other aquatic life.
Option A is incorrect because it is the opposite of what happens during eutrophication. Algal growth increases during eutrophication, not decreases.
Option B is incorrect because it is not a characteristic of eutrophication. Dissolved oxygen levels can decrease during eutrophication, but this is not the result of excessive availability of oxygen.
Option C is incorrect because it is not a characteristic of eutrophication. Dissolved nutrients can increase during eutrophication, but this is not the result of loss of nutrients from the water.