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EPA-approved water quality 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.

Our assessment updated fresh and marine water listings. We also updated how we map polluted rivers, lakes, and streams — moving from a land-based to a water-based system.

This latest approved assessment also uses an enhanced mapping platform 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.

We're required to identify polluted waters

This assessment fulfills our obligation under the federal Clean Water Act (CWA) §303(d) and §305(b) to identify polluted waters — known as the 303(d) list — as well as report on the status of water quality statewide where data is available.

About the current water quality assessment approved by the EPA

This assessment updated freshwater listings based on data collected between 2000 and 2010. We updated how we map polluted rivers, lakes, and streams.

We moved 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.

Water Quality Atlas

The current water quality assessment is available on an enhanced mapping platform called the Water Quality Atlas. The Water Quality Atlas is an interactive search and mapping tool that includes multiple layers of information.

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.