The Water Quality Standards are the basis for protecting and regulating the quality of surface waters in Washington. The standards implement portions of the federal Clean Water Act by specifying the designated and potential uses of waterbodies in Washington State. They set water quality criteria to protect those uses and acknowledge limitations. The standards also contain policies to protect high quality waters (antidegradation) and in many cases specify how criteria are to be implemented, for example in permits.

The water quality standards are established to sustain public health and public enjoyment of the waters and the propagation and protection of fish, shellfish, and wildlife. This three-part approach was designed to set limits on pollution in our lakes, rivers and marine waters in order to protect beneficial uses such as aquatic life, swimming and fishing.  They also support other water protection processes (such as total maximum daily loads, also known as TMDLs, and the biannual water quality assessment), and guide Washington citizens, businesses and other government agencies to the goal of sustaining clean water for current and future use.  The three-part approach covers:
 

• Designated uses, such as fishing, swimming, and aquatic life habitat.
   
• Numeric and narrative water quality criteria limits to protect the uses.
   
• Policies, such as antidegradation, to protect higher quality waters from being further degraded.