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How do chemical fertilizers and pesticides affect nearby waterways?

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A green cotton combine harvests a field of mature cotton plants, with white cotton bolls visible across the landscape. — Agricultural technology Cotton combine harvesting a cotton field.

Chemical fertilizers and pesticides significantly degrade nearby waterways through agricultural runoff, which acts as a dispersed source of pollution that is difficult to control.1

Impact of Fertilizers

Fertilizers introduce excess nutrients, primarily nitrogen and phosphorus, into aquatic ecosystems. This leads to eutrophication, a process where these nutrients trigger excessive growth of algae and aquatic plants. As these organisms die and decompose, they consume vast amounts of dissolved oxygen, creating hypoxic "dead zones" where fish and other wildlife cannot survive. Additionally, high levels of nitrates and nitrites in groundwater can pose direct toxicity risks to humans and livestock.234

Impact of Pesticides

Pesticides, including insecticides, herbicides, and fungicides, enter water bodies through drainage and runoff. These chemicals can be lethal to nontarget aquatic life, such as fish in farm ponds. While some pesticides attach to suspended sediments and settle out of the water, persistent chemicals—such as certain chlorinated hydrocarbons—can remain in the environment, accumulating in the food chain and causing long-term harm to wildlife and human health.56

Responsible management of these inputs is essential to protecting the integrity of our shared water resources.25