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Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Avenue, Suite 1000, Portland, OR 97204

Water Quality

photo of Fanno CreekThe Oregon Department of Environmental Quality (DEQ) establishes total maximum daily loads (TMDLs) for state waterways. TMDLs identify the maximum amount of a pollutant the water body can assimilate without violating water quality standards. Water quality standards for the Tualatin River, into which all creeks in the Fanno Creek Watershed flow, are temperature, bacteria, dissolved oxygen, and phosphorus.
 
Water temperature has a large impact on the types of organisms found in a water body. Cool water is a basic requirement for native salmon, trout, some amphibians, and other cold water aquatic species. Growth and reproduction are adversely affected when water is too warm. Temperature also plays a role in dissolved oxygen concentration, which is important for fish survival. The colder the water, the greather the amount of oxygen that can be dissolved in it.   
 
Low dissolved oxygen (DO) is one of the limiting factors for cold water fish, including salmonids. Fish use oxygen when it is transported across the gill by diffusion. This process relies on the difference in concentration of DO in the water versus the fish.
 
Standards for bacteria concentration are set to protect people from contact with and ingestion of pathogenic bacteria, which can occur during recreational activities such as swimming and boating. Contact with these bacteria can cause skin and respiratory ailments and gastroenteritis.
 
Phosphorus is a nutrient that causes algae growth. The decomposition of excessive algae can lower DO levels, which can affect fish populations. Natural phosphorus leaches into the creek from the ground and is also added to the environment by fertilizers. Additionally, phosphorus in area soils can reach streams in stormwater runoff, increasing total suspended solids (TSS) and phosphorus levels in streams.
 
Other water quality concerns in Fanno Creek include sediments and nutrients, especially during storm events. Increased sedimentation may result from development and removal of vegetation, landslides onto roadways and into watercourses, and streambed and streambank erosion caused by increased stormwater runoff. Excess nutrients probably are associated with runoff from landscaped residential areas and with sediments.
 
City modeling identified hot spots that may be responsible for generating more pollutants than other areas within the watershed. The city may prioritize these areas for pollutant reduction, and areas of low pollutant loading could be targeted for protection.
 
Other findings include:
  • Areas with concentrations of commercial and multifamily land uses show up as areas with higher potential pollutant loads. 
  • The major transportation corridors (e.g., Interstate 5) and associated commercial development show up as areas with higher potential pollutant loads.
  • The street systems tend to show higher potential loadings.
Fanno Creek Mainstem
Water quality in Fanno Creek is impaired by stormwater runoff from existing sources and development. Summer in-stream temperatures exceed the water quality standard of 64 degrees Fahrenheit necessary to protect salmon. E. coli levels exceed the water quality standard in 50% of samples in summer and 25% during winter. Fanno Creek was ranked as poor on the Oregon Water Quality Index due to high levels of nutrients, total solids, and bacteria. High silt and sediment loads are transported from upland urban sources to the stream and accumulate in lower portions of the subwatershed. Channel erosion also contributes to high levels of total suspended solids (TSS).
 
Pendleton Creek
Little water quality data are available for Pendleton Creek. Stormwater runoff from development may contribute a number of pollutants. Monitoring indicates that E. coli levels exceed the water quality standard in 50% of samples in summer and 10% during winter.
 
Vermont Creek
Water quality in Vermont Creek is impaired by stormwater runoff from development. E. coli levels exceed the water quality standard in 50% of samples in summer and 25% during winter. Summertime phosphorus concentration is far above background levels. Vermont Creek was ranked as very poor on the Oregon Water Quality Index due to high levels of nutrients, total solids, and bacteria. High silt and sediment loads are transported from upland urban sources to the stream and accumulate in lower portions of the subwatershed. Channel erosion also contributes to high levels of total suspended solids (TSS). These pollutants tend to increase in concentration in lower portions of the creek, and may contribute to water quality problems downstream in Fanno Creek.
 
Woods Creek

Water quality in Woods Creek is impaired by stormwater runoff from development. Summer in-stream temperatures exceed the water quality standard of 64 degrees Fahrenheit for salmon protection. E. coli levels exceed the water quality standard in 50% of samples in summer and 10% during winter. Woods Creek was ranked as poor on the Oregon Water Quality Index due to high levels of nutrients, total solids, and bacteria. High silt and sediment loads are transported from upland urban sources to the stream and accumulate in ower portions of the subwatershed. Channel erosion also contributes to high levels of total suspended solids (TSS). These pollutants tend to increase in concentration in lower portions of the creek and may contribute to water quality problems downstream in Fanno Creek.

 
North Ash Creek
Little water quality data are available for North Creek. Stormwater runoff from development may contribute a number of pollutants. Monitoring indicates that E. coli levels exceed the water quality standard in 50% of samples in summer and 10% during winter.
 
South Ash Creek
Little water quality data are available for South Creek. Stormwater runoff from development may contribute a number of pollutants. Monitoring indicates that E. coli levels exceed the water quality standard in 10% of samples in summer and winter.
 
Red Rock Creek
No specific water quality data for Red Rock Creek is available. However, stormwater runoff from development in this subwatershed may contribute to water quality problems downstream in Fanno Creek.