NOTICE: Ecology's web applications will be unavailable Wednesday, Nov. 29 from 5:30 to 7:30pm, for scheduled maintenance.

Water Quality photo identifier

Water Quality Program

Tumwater Falls photo.  Author unknown.


The federal Clean Water Act, adopted in 1972, requires that all states restore their waters to be “fishable and swimmable.” Section 303(d) of the Clean Water Act established a process to identify and clean up polluted waters. Every two years, all states are required to perform a water quality assessment of the quality of surface waters in the state, including all the rivers, lakes, and marine waters where data were available. Ecology compiles its own water quality data, and invites other groups to submit water quality data they have collected. All data submitted needs to be collected using appropriate scientific methods.

The assessed waters are placed in categories that describe the status of water quality. Once the assessment is complete, the public is given a chance to review it and give comments. The final assessment is formally submitted to the Environmental Protection Agency (EPA) for approval.

303(d) List

Waters whose beneficial uses  – such as for drinking, recreation, aquatic habitat, and industrial use – are impaired by pollutants are placed in the polluted water category on the water quality assessment. These water bodies fall short of state surface water quality standards and are not expected to improve within the next two years. The 303(d) list, so called because the process is described in Section 303(d) of the Clean Water Act, comprises waters in the polluted water category.

Ecology’s assessment of which waters to place on the 303(d) list is guided by federal laws, state water quality standards, and the Policy on the Washington State Water Quality Assessment. This policy describes how the standards are applied, requirements for the data used, and how to prioritize TMDLs, among other issues. In addition, even before a TMDL is completed, the inclusion of a water on the 303(d) list can reduce the amount of pollutants allowed to be released under permits issued by Ecology.

The goal is to make the best possible decisions on whether each body of water is impaired by pollutants, to ensure that all impaired waters are identified and that no waters are mistakenly identified.

The water quality assessment and Water Quality Improvement Projects

Waters placed on the 303(d) list require the preparation of a water cleanup plan, like a total maximum daily load (TMDL) or other approved water quality improvement projects. The TMDL identifies how much pollution needs to be reduced or eliminated to achieve clean water. It identifies the maximum amount of a pollutant to be allowed to be released into a water body so that the beneficial uses of the water are not impaired. The TMDL allocates that amount of the pollutant among various sources.

Why is the water quality assessment so important?

The assessment helps us to use state resources more efficiently by focusing our limited time on water bodies that need the most work. The list of water bodies in the assessment reflects local government, community and citizen recognition of water quality problems in Washington, demonstrating citizen interest in and commitment to clean water. When citizens are involved in the process of assessing water quality, they will want to be involved in actions to improve water quality.

Contact us for more information


Back to top of page

Last updated August 2016