Adequate riparian (streamside) vegetation is a vital part of good water quality. Vegetation controls water pollution by providing cooling shade, minimizing streambank erosion, and filtering sediments and nutrients from overland flows. It also slows water flowing across the land so it has an opportunity to soak into the soil rather than running off into the stream.

In Multnomah County, agricultural activities must allow the establishment, growth, and maintenance of sufficient streamside vegetation to provide these functions. The best way to protect water quality is to keep the existing native vegetation. In areas that lack vegetation, control invasive plants and plant appropriate native vegetation. Plants must also be protected from grazing animals. Fencing livestock away from the riparian area is a great way to protect the plants. Provide water for livestock at a small access on the stream or better yet, at a nose pump or trough in the pasture. Horses and livestock will be healthier if they have access to clear, unpolluted water.