The existence of riverside vegetation is also important to the health of the species that live within the river. Specifically, this vegetation helps maintain a river's health by influencing the amount and kind of sediment in the river. Riverside vegetation does this by anchoring soil, catching silt, filtering out pollutants, and absorbing nitrogen and phosphorus. Such vegetation also helps provide shade that cools the water and provides habitat for insects and their predators. The effect of too much sedimentation can be seen when vegetation along riverbanks is removed by flooding or another event.
Sediment washes back into the water, causing turbidity.
Turbidity occurs when sediment is stirred up and suspended in water, and in a river can impair the respiration of fish or other aquatic organisms. Turbid conditions can also cause sediment to cover gravel used for fish-spawning, raise the temperature of the water, and bury submerged plants. A tributary is a river or stream that feeds into a larger body of water. The Snake River, originating in Yellowstone Park and joining the Columbia near Hanford, is the Columbia's largest tributary. As water flows downstream, organic debris including decomposing organisms and leaves collect and provide nutrients to plants, fish, and wildlife.