What is a common environmental risk of excessive phosphates in freshwater systems?

• A. They reduce water hardness.
• B. They promote algal blooms and oxygen depletion.
• C. They increase salinity.
• D. They stabilize sediments and prevent erosion.

Answer: (B)

Nutrient pollution from phosphates in freshwater systems mainly leads to algal blooms that deplete oxygen. When phosphates act like fertilizer, they fuel rapid growth of algae and other aquatic plants. Dense algal blooms can block light and disrupt normal underwater communities. When these organisms die, bacteria break them down and consume large amounts of dissolved oxygen in the water, leading to hypoxic conditions that stress or kill fish and other aquatic life. This sequence—phosphate-driven growth followed by oxygen depletion—is a common environmental risk of excess phosphates in freshwaters. Phosphates don’t directly change water hardness, salinity, or sediment stability in the way described by the other options.