Trees are an essential and integral part of the riparian zone. When trees, shrubs, and other plants cover a stream's floodplain, they slow the rush of high water . Since fast-moving water can carry a higher amount of soil particles than slower water, sediments are dropped by the flood waters in the riparian zone rather than ending up downstream in reservoirs, channels, and harbors. Slowing the water also helps reduce bank erosion. Trees shade creeks and rivers and help keep the water cool .
Cool water carries more oxygen and provides a more livable environment for many species of fish.
Warmer water of denuded creeks also slightly increases the release rate of pollutants from sediment particles. Riparian zones with trees and other vegetation filter excessive chemicals that wash from lawns, gardens, and fields. In some cases, such as phosphates that cling to soil particles and move down slope in runoff water, the soft soil and leaf litter of the riparian zone act as a trap for the particles. The phosphates stay on-site, absorbed into the soil from which they are taken up by tree roots. Nitrates move either on the surface or in groundwater.