The natural stream management areas overlay shows river and stream reaches with HNC and aquatic biota values because of the presence of indigenous vegetation on either side of the watercourse. The presence of indigenous vegetation of a minimum qualifying length and width, indicates that the river or stream has good ecological values, particularly as habitat and breeding areas for native fish. The presence of indigenous vegetation means that the stream bed is usually unmodified, allowing the movement of fish up and down the stream, as well as providing natural places for fish to feed and shelter. The presence of vegetation on the bank provides food for fish, keeps water temperatures constant and filters contaminants and sediments reducing the levels entering the stream. Many of these natural stream management areas are found in the upper reaches of a catchment, or in reserve areas and water quality is generally high. The combination of suitable temperature, pH and water quality and the presence of native aquatic plants and aquatic fauna are collectively referred to as "in-stream values".