While we tend to focus on the portion of the stream that carries the water (stream channel) it is actually the watershed that determines the quality of water in that channel.
A high quality watershed must have riparian areas covered with grasses, forbs (flowering plants) and trees to filter and allow infiltration of water, prevent erosion along the bank, and function as wildlife corridors. This riparian cover also provides essential shade to moderate water temperatures. Higher oxygen levels occur in cooler waters which is beneficial to aquatic species.
Meandering streams are a very important characteristic of a healthy watershed. Meanders slow the water allowing the sediments to settle out along the banks, thereby reducing turbidity. This slowing of the water also decreases damage from flooding.
Biological diversity is another extremely valuable component of a healthy watershed for both the natural system and human use. Biological diversity is an indicator of high quality water as many species cannot survive in watersheds that contribute to polluted waters.
Find opportunities to enjoy walks along streams and evaluate their health by checking for these characteristics. You can find more information about watersheds and how you can contribute to their health at www.sgrwa.org.