Napa County Resource Conservation District
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Healthy Stream Environments

Healthy stream environments have characteristics which will support aquatic life. Most organisms adapted to live in streams need cool, clean water with a high content of oxygen and adequate food sources to survive. Stream organisms also need diverse habitat. These characteristics are obtained if a stream system has certain components.

Vegetation along the sides of streams (called the riparian area) shades creeks to keep temperatures cool. This stream side vegetation also plays a role in keeping stream water clean. Sediment in a creek is considered a pollutant since it kills many of the organisms in the water by smothering them. Sediment can also inhibit creek creatures´ ability to find food. Stream side vegetation of the riparian area stabilizes the banks, helping to control erosion of sediment into the water.

Vegetation on stream banks also contributes to the food chain by providing leaf litter that feeds many aquatic invertebrates. The aquatic invertebrates in turn are eaten by organisms like birds, frogs, and fish which are higher up in the food chain.

Streams with fast flowing waters usually have sufficient amounts of dissolved oxygen for stream inhabitants. As the water cascades down slopes and over boulders and rocks in the stream, oxygen from the air enters the stream system. Cool water can hold more oxygen than warmer water, so cool streams will be better able to support aquatic life.

Stream organisms need to be able to find places to hide from predators, forage for food, reproduce, and rest. Streams with diverse habitat will provide for all these needs. Diverse habitat is provided by structures in the stream like large logs, tree roots, boulders, and undercut banks. Stream bottoms in healthy creeks have a mixture of substrate materials including sand, gravel, cobble, boulders, and bedrock. Fine sediment covering the stream bottom over large areas are a sign that excess sediment is entering the stream system. It is also important that the physical structure of a stream is such that there are varying depth regimes. This means that there are deep pools, as well as shallow areas.

Human activities can have an impact on a stream´s physical and chemical characteristics. Streams are diverted, dammed, and straightened. Removal of vegetative cover and disturbance of the soil cause erosion carrying sediment into creeks. Water diversions upstream result in lower flows with higher temperatures. Runoff from farms, homes, livestock, industry, and roads may carry heavy nutrient loads and chemical pollutants into stream waters. It is important to keep existing stream habitat and water quality as healthy as possible. In streams experiencing disturbance, restoration projects and land management changes can help to restore balance to the system.

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