Nutrients are pollutants of concern because they can lead to eutrophication.
Eutrophican is a term used to describe an excess of nutrients that can stimulate an explosive growth of algae or an algal bloom in surface water. This increase in algae will cause the water to become low in dissolved oxygen. Low dissolved oxygen and toxic algae blooms can lead to fish kills, toxic shellfish poisoning, and other public health issues. All of these affects combined can select for only certain species of fish that are low-oxygen tolerant species and decrease fish diversity.