What effect does excess nitrogen in water have?

Excess nitrogen in water typically plays a significant role in promoting algae growth, a process known as eutrophication. When nitrogen levels are too high, it become a nutrient that fuels the rapid growth of algae in aquatic environments. This can lead to harmful algal blooms, which can produce toxins detrimental to aquatic life, impact water quality, and interfere with recreational activities.

The phenomenon occurs because nitrogen is one of the key nutrients that plants and algae use for growth. In natural environments, a balance of nutrients is essential; however, when nitrogen (often sourced from agricultural runoff, wastewater, and fertilizers) is in surplus, it disrupts this balance, leading to excessive algae proliferation. The subsequent decay of the algae can deplete oxygen levels in the water, resulting in dead zones where aquatic life cannot thrive.

In contrast, enhancing drinking water quality, improving fish reproduction, and increasing water clarity would generally stem from balanced nutrient levels, not from an excess of nitrogen. Hence, the correct choice emphasizes the significant impact of nitrogen on aquatic ecosystems by fostering algal overgrowth rather than supporting healthier water conditions.