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How do fertilizers and pesticides pollute rivers and groundwater?

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water rapids, Niagara Falls, Canada — water Water is the most plentiful compound on Earth and is essential to life. Although water molecules are simple in structure (H₂O), the physical and chemical properties of water are extraordinarily complicated.

Fertilizers and pesticides degrade water quality through runoff and leaching, processes that pose significant risks to both surface water and groundwater systems.12

Impact on Rivers and Surface Water

Agricultural runoff carries excess fertilizers—primarily nitrates and phosphates—into rivers and lakes. These nutrients trigger cultural eutrophication, fueling rapid algal blooms. As these blooms die and decompose, microorganisms consume the water's dissolved oxygen, leading to hypoxia and the death of aquatic life. Additionally, pesticides (including herbicides and insecticides) can enter watercourses through drift or drainage, introducing toxic chemicals that harm fish and other organisms.3145

Impact on Groundwater

Groundwater is highly susceptible to contamination because it is often recharged by the leaching of surface materials. When fertilizers and organic pesticides are applied to soil, they can percolate downward through the subsurface. This process increases the concentration of ammonium, phosphates, and chemical residues in groundwater, potentially compromising the safety of these vital water resources.2

Protecting our water supplies is a fundamental ethical responsibility, as these ecosystems are essential for sustaining life and supporting human health.31