How Excess Nutrients Harm Streams

In streams and rivers, too much algal growth resulting from high levels of nutrients may degrade the physical habitat of the waterway and may directly affect the health of fish and other aquatic life. For example, heavy growths of algae in streams may form dense mats on the water surface or on the stream bottom. These algal mats reduce the amount and diversity of shelter and nursery areas for small fish and aquatic invertebrates, such as mayflies and crayfish. Algae floating in the water may shade the bottom, thus reducing the growth of important submerged plants rooted on the bottom. In addition, nutrients from non-point source runoff are often associated with high levels of suspended sediments eroded from the land surface or stream banks. These suspended sediments degrade water quality by clouding the water, making it difficult for aquatic organisms to breathe and find food. These suspended sediments settle and smother bottom habitats where aquatic invertebrates and fish find shelter. Streams and small creeks are often the initial receptors of pollutants, which then travel downstream to the bays.