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? The watershed is the area of land where all the water that is under it or drains off of it flows into the same place.
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 and that 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.
Another feature of healthy watersheds is biological diversity. A diversity of plant and animal species within the natural systems of the watershed is an indicator of high quality water because many species cannot survive in polluted streams, lakes, and rivers. Waterways in a watershed with significant natural systems intact are also healthier for human use as such residential use, swimming, boating and fishing.
Find opportunities to enjoy walks along streams, to learn about them and to check their health by looking for these characteristics. You can find more information about watersheds and how you can contribute to their health at www.sgrwa.org.