Stream Water Quality and the Influence of Temperature

Streams, in their natural state, are typically diverse and biologically productive environments. Streams impacted by urbanization often experience degradation brought about by the cumulative effects of flow alteration (i.e., an increase in the amount of stormwater runoff). One of the water quality parameters affected by urbanization is stream temperature. Research shows that shading provided by riparian vegetation (i.e., the area directly adjacent to a stream), groundwater discharge, and stream width have the greatest influence on stream temperature. These variables are highly influenced by land use.

Aquatic life is temperature-sensitive and requires water that is within a certain temperature range. When temperature exceeds tolerance levels, cold-water organisms, such as salmon, become physically stressed and have difficulty obtaining enough oxygen. Prolonged exposure to temperatures outside their tolerance range will likely cause mortality.

Generally speaking, any fish's body temperature is about 1o F (0.5o C) higher than the temperature of the water it lives in. With this strong dependence on the temperature of the surrounding environment, it is easy to see the importance of temperature in aquatic ecosystems.

Wooded riparian zones can reduce stream temperatures, particularly in terms of maximum temperatures. Conserving and restoring wooded riparian zones provides benefits in terms of mitigating some of the ecological effects of climate change on water temperature.

High water temperatures present one of the biggest challenges to healthy aquatic ecosystems in the Willamette Basin. The entire mainstem Willamette and many tributaries suffer from impaired water quality due to high temperatures. Many of the aquatic organisms important to us are dependent on cold water – particularly salmon, trout, and many types of aquatic insects. Human disturbance has a great impact on temperature through direct thermal pollution and loss of streamside vegetation.
To help reduce stream temperature and pollutants the City of Wilsonville is offering up to five native tree seedlings for any community member or business within the City limits, for planting on their property. Plantings along streams and other water bodies are encouraged, but any tree planting enhances the City’s ‘urban forest’ and contributes to reducing stream temperature and pollutants. The trees are obtained at a local nursery, which provides input on their selection, planting and care. Arrangements can be made for delivery if a customer is not able to pick them up at the nursery.

For more information and to obtain a tree coupon, contact Luke Bushman, Stormwater Management Coordinator, at 503-570-1552 or

Pedestrian Bridge over Boeckman Creek - Memorial Park
Pedestrian Bridge over Boeckman Creek - Memorial Park