Tryon Creek and its tributaries within the City of Portland are small headwater streams located within an urban environment. They exhibit many of the characteristics typical of urban streams, including altered flow patterns and degraded water quality. These characteristics result from changes in hydrology and increased pollutant loadings from urban development.
Water Quality Concerns in the Tryon Creek Watershed
- Stream temperatures do not meet state standards in the summer. The elevated temperatures are likely caused by very low streamflows during the summer months, warmer air temperature resulting from urban heat island effects, reduced riparian vegetation (and consequent lack of stream shading), and stormwater runoff from impervious surfaces exposed to sunlight.
- Bacteria levels sometimes do not meet standards. Potential bacteria sources include both human sources (illegal sanitary connections, dumping to storm drains, failing septic systems) non-human sources (birds, dogs, cats, raccoons, and other animals).
- Elevated levels of suspended sediments and nutrients (phosphorous and nitrogen), especially during storm events. Sediment smothers fish spawning beds and transports a variety of pollutants, such as oil, grease, metals and pesticides. Excess nutrients can contribute to low dissolved oxygen levels in the creek, which is harmful to fish. Sedimentation may result from vegetation removal, landslides, and erosion caused by increased stormwater runoff. Excess nutrients are probably associated with sediments and with runoff from landscaped residential areas.
- Stormwater carries pollutants from upland land uses, including residential areas and transportation corridors such as Interstate 5, Barbur Boulevard, and Terwilliger Boulevard.