What are the sources of excess nitrates and phosphates in rivers?

Excess nitrates and phosphates in rivers primarily originate from agricultural runoff, where fertilizers containing these nutrients are applied to crops and subsequently washed away by rainwater. Other significant sources include wastewater discharges from sewage treatment plants and industrial facilities, as well as urban runoff containing fertilizers from lawns and gardens. Additionally, livestock waste can contribute to nutrient loading in nearby water bodies. Together, these sources lead to nutrient pollution, which can cause harmful algal blooms and degrade water quality.