Water quality assessment & 303(d) list

The federal Clean Water Act requires states to perform a water quality assessment every two years to track how clean the rivers, lakes, and marine water bodies are. We place assessed water bodies in categories that describe the quality of the water and status of any needed cleanup. The assessment helps us use state resources more efficiently by focusing our limited resources on water bodies that need the most work.

2022 Water Quality Assessment call for data

We are beginning our next update to the Water Quality Assessment and we need recent water quality data from Washington’s rivers, streams, lakes, and marine waters. We are seeking data collected between January 1, 2012 and December 31, 2021.

To make sure your data is included in this next Water Quality Assessment, please submit before September 30, 2022. Water quality data can be submitted to Ecology's Environmental Information Management (EIM) database. Narrative information and studies, such as published research and peer-reviewed reports, can be submitted directly to Water Quality Assessment staff at 303d@ecy.wa.gov.

All data submitted must have been collected under a quality assurance project plan, or similar guidance document. Data must be representative of ambient water quality conditions. Submitters must be able to confirm that quality assurance procedures were followed and must be prepared to provide a copy of the plan upon request. If you previously submitted data to us, you do not need to submit it again.

View our online database for the latest assessment results.

2018 Water Quality Assessment submittal to EPA

The 2018 Water Quality Assessment was submitted to EPA for approval on Aug. 31, 2021. This version of the assessment can be viewed through the Candidate Water Quality Assessment Review search tool or map tool

See the timeline below for more information about how we developed this Water Quality Assessment.

EPA decision

On June 8, 2022, EPA issued a partial approval of our 2018 Water Quality Assessment. EPA is currently seeking public comment on portions of the Water Quality Assessment that they disapproved.

We proposed placing certain impaired waterbodies in Category 4A (impaired with a cleanup plan or TMDL) rather than Category 5 (impaired without a cleanup plan), because these waterbodies were within the boundary of an already existing TMDL. EPA did not approve some of these proposed changes to Category 4A because they said there was not enough information to support the change. EPA is taking comments on their decision to keep these specific listings in Category 5. For more information or to provide comment on their decision, visit EPA’s website.

Draft assessment documents

What is the water quality assessment?

The water quality assessment is our process of collecting data and assessing the quality of surface water in the state. This includes all rivers, lakes, and marine water. You can view the results of the assessment in our online database.

The federal Clean Water Act requires that all states restore their water bodies to be “fishable and swimmable.” Section 303(d) of the Clean Water Act establishes a process to identify and clean up polluted water.

What is the Water Quality Atlas?

We also have a mapping tool called the Water Quality Atlas. The Water Quality Atlas is an interactive search and mapping tool that includes additional layers of information in an easy-to-use mapping application.

Users can map the water quality assessment category results, view water quality standards for a location, identify areas addressed by Total Maximum Daily Loads (TMDLs), and see permitted wastewater discharge outfalls.

The current assessment

The current water quality assessment — called the 305(b) report and 303(d) list of impaired waters for the state of Washington — was approved by the U.S. Environmental Protection Agency (EPA) on July 22, 2016. See below for more information about the current process to update the assessment. 

Read the 2016 EPA approval letter.

Key changes that were made in 2016

  • Updated freshwater listings based on data collected between 2000 and 2010.
  • Updated how we map polluted rivers, lakes, and streams — moving from a land-based system (township/range/section) to a water-based (National Hydrography Database) system. The mapping change helps us be consistent with other agencies and states, and is strongly recommended by EPA.

The process to update the Water Quality Assessment

The following timeline provides information on each step of the current assessment cycle. Because we have been working on a large data automation project (see Assess the data section below) we have not submitted an assessment since 2016. However, this automation of our data should now allow us to meet our requirement for submittal every two years. This new assessment will serve as Washington's past due submittals.

The opportunity for early tribal review of the assessment is part of a 1997 cooperative agreement between the tribes, Ecology, and EPA that recognizes the government-to-government relationship between Washington and tribes in managing water quality.


Woman kneeling next to stream holding water sampling bottle

How are water bodies assessed?

We compile our own water quality data, and invite other groups to submit water quality data they have collected. We only assess data that meets high quality assurance and credible data requirements. Our goal is to accurately determine if water bodies are polluted based on the best available data.

The assessed water bodies are placed into one of five categories that describe the water quality.  Once the assessment is complete, we provide the public a chance to review and give comments. We submit the final assessment to the Environmental Protection Agency for approval of the category 5 listings, also called the 303(d) list.

Assessment categories


303(d) list

Water bodies whose designated uses (such as for drinking, recreation, aquatic habitat, and industrial use) that are impaired by pollutants are identified in the water quality assessment as "Category 5: Polluted water that requires a water improvement project." The 303(d) list, so called because the process is described in Section 303(d) of the Clean Water Act, lists water bodies in the polluted water category.

Federal laws, state water quality standards, and water quality assessment policy 1-11 guide our assessment of which water bodies to place on the 303(d) list.

To view the list, go to the water quality assessment database and select Category 5 (under Categories).

What happens to polluted water bodies?

If water bodies are polluted, we develop a water cleanup plan, also called a Total Maximum Daily Load or TMDL, to reduce pollution sources throughout the surrounding watershed. After pollutant controls are in place, we monitor in the watershed to see if the water meets state water quality standards.

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