Nitrates
Nitrogen exists in the environment in many forms. In recent decades, there has been a substantial increase in nitrogen fertilizer use. Nitrogen can affect drinking water. Elevated nitrate-nitrogen in the Minnesota River can pollute aquifers it recharges. At high enough concentrations, nitrate-nitrogen can cause infants who drink the water to become sick (methemoglobinemia). Downstream, nitrate-nitrogen from the Minnesota River contributes to hypoxia (low levels of dissolved oxygen) in the Gulf of Mexico by stimulating the growth of algae which, through death and decay, consume large amounts of dissolved oxygen and thereby threaten aquatic life.