The primary issue with the overuse of fertilizers in U.S. agriculture is runoff causing algal blooms, which harms water quality and ecosystems.

Runoff from excessive fertilizer use in American agriculture can introduce surplus nutrients, especially phosphorus and nitrogen, into adjacent water bodies. Algal blooms are caused by this discharge, where an overabundance of algae reduces the amount of oxygen in the water, resulting in "dead zones" that are detrimental to aquatic life. Toxins released by algae blooms can also damage fish populations and the quality of drinking water. The issue is most acute in agricultural areas close to lakes, rivers, and the ocean. Mitigating the environmental impact of excessive fertilizer usage requires reducing fertilizer use, implementing precision agriculture techniques, and enhancing nutrient management.