Untreated sewage triggers nutrient pollution in lakes

Steps:

• Untreated sewage contains high levels of nitrogen and phosphorus from human waste.
• These nutrients enter the lake and fertilize algae growth.
• Algal blooms proliferate, blocking sunlight and depleting oxygen.
• This leads to eutrophication, harming aquatic life.

Why B is correct:

• Eutrophication is defined as the process where nutrient enrichment from sewage causes excessive algae growth, oxygen depletion, and ecosystem imbalance.

Why the others are wrong:

• A: Biodiversity decreases due to oxygen loss killing diverse species.
• C: Fish populations decline from low oxygen and toxic algal blooms.
• D: Light penetration decreases as dense algal blooms cloud the water.

Final answer: B