Water Quality in the Stillaguamish River Basin


The Stillaguamish River and many of its tributary streams exceed Washington State water quality recreational contact standards for fecal coliform bacteria. That means it can be unsafe for you, your family members, and your pets to come in contact with these waters. In addition, fecal coliform bacteria levels impact classification of shellfish beds and high levels can lead to restricted or prohibited harvest in nearby shellfish growing areas.

Sources of Fecal Coliform Bacteria Diagram

Fecal coliform is a widely used indicator of the presence of other organisms that can cause illnesses such as typhoid, cholera, dysentery and hepatitis A. Fecal coliform is bacteria found in the feces of warm blooded animals including humans and other mammals. Sources of fecal bacterial pollution in the CWD include human sewage, livestock, pets, and wildlife.

Water Quality Standards

The federal Clean Water Act requires all states restore waterways to be “fishable and swimmable.” Water quality standards, defined by the Washington State Department of Ecology (Ecology), are the basis to restore, protect and regulate the quality of surface waters for aquatic life, public health and the use and enjoyment of our waters. Each water quality parameter has criteria set forth for fresh water and marine water.

Detailed information on water quality standards can be found in the Ecology Water Quality Standards for Surface Waters of the State of Washington.

Ecology compiles water quality sampling results and assesses fresh and marine waters for compliance with water quality standards. Those that do not meet standards are placed on the 303(d) list. View a description of the process and tools to locate waters exceeding fecal coliform standards.

Water quality clean-up plans or Total Maximum Daily Load (TMDL) plans are developed and implemented for waters placed on the 303(d) list. The Stillaguamish River Multi-Parameter TMDL describes the problems and actions stakeholders, including the public, can take to improve water quality.

Water Quality Monitoring

Water Quality Assessment by Snohomish County

In 2007, Snohomish County published the State of the Stilly Report (PDF) summarizing conditions and trends associated with County sampling locations in the Stillaguamish Watershed. An improving trend was observed for some stream and river segments partially due to wastewater treatment plant upgrades, dairy waste management, and septic system maintenance. While these sites demonstrated improvement for certain parameters, such as fecal coliform and dissolved oxygen, the report notes that many still did not meet water quality standards.

In 2011, Snohomish County began using the Stillaguamish Microbial Water Quality Assessment (MQWA) (PDF) methodology to identify sources of point and non-point pollution that require corrective action. Water quality data for ten year periods have been analyzed in order to assign each stream or river basin a “rank” corresponding to the level of bacterial pollution. The maps on the right show the locations of water quality sampling sites and their respective MWQA “ranks.” The first map shows the results for the 2001-2010 ten year period and the next map shows the results for the 2005-2015 ten year period. During these two periods, the Portage Creek, Church Creek, and Lower Stillaguamish sub-basins exhibited the highest fecal coliform levels and have been identified by stakeholders as priority areas where Snohomish County and partners should implement a focused pro-active approach to identify and correct potential bacterial pollution sources.


Stilly MWQA Ranking - Fecal Coliform Sampling Stations


Stilly MWQA Ranking Sampling Stations, 2005-2015

Water Quality Resources