The correct answer is B. Eutrophication.
Eutrophication is the enrichment of water bodies with nutrients (mainly phosphorus and nitrogen) that stimulate the growth of excessive plant life. This excess plant life can deplete the water of oxygen, leading to the death of fish and other aquatic organisms. Eutrophication can also lead to the formation of harmful algal blooms, which can produce toxins that can be harmful to humans and animals.
A. Succession is the process by which an ecosystem changes over time, as different species colonize and become dominant.
C. Stratification is the separation of a water body into layers of different densities, due to differences in temperature, salinity, or dissolved substances.
D. Climax vegetation is the final stage of ecological succession, in which the community of organisms is in equilibrium with its environment.