Which statement best describes oligotrophic water?

• A. Oligotrophic water is water with low nutrients, clear water, and high dissolved oxygen.
• B. Oligotrophic water has high nutrients and abundant algae.
• C. Oligotrophic water is water with moderate nutrients and moderate dissolved oxygen.
• D. Oligotrophic water has high salinity and low clarity.

Answer: (A)

Oligotrophic water is defined by very low nutrient levels, which keeps the water clear and highly oxygenated. When nutrients are scarce, algal and aquatic plant growth remains limited, so the water stays transparently blue or greenish and light penetrates deeper. With less biological demand and photosynthesis occurring at a modest pace, dissolved oxygen tends to stay high, especially in the upper layers. Therefore, the statement that oligotrophic water has low nutrients, clear water, and high dissolved oxygen best captures this condition. The other descriptions describe environments with more nutrients and algae (eutrophic), or with factors like salinity and clarity not tied to nutrient-driven productivity.