In the State of Washington, as in many others, some of the best information for wild trout anglers originates in the water quality world.

In the mid-2000s, Washington adopted surface water classifications based on "designated" uses.  The sensible idea behind such classifications is that, for example, the regulations governing what you can do in a headwater stream that is spawning habitat for an endangered salmonid species ought to be quite different from a warm-water, 8th-order river that flows through agricultural land.  In this scheme, you can designate a use for one stream as "salmonid spawning" and the other as "agricultural irrigation", and apply different rules.

Among Washington's designated uses were spawning habitat for salmonids and "core habitat", essentially rearing or resident habitat for salmonids including both anadromous species like salmon and steelhead as well as resident trout (both native and exotic). The regulations call-out "char" water (requiring even colder water, and protecting the endangered bull trout) separately from other salmonids.

During the analysis that accompanied the promulgation of these new regulations, the USEPA decided that Washington's designated uses didn't protect all of the water that should be, and prepared a state-wide series of maps showing the differences.   What is unique about these maps is a) they're state wide, and b) are really the only comprehensive source that includes resident trout.  A detail from one map is shown below.  Explanation of the color coding follows below the image.

In the map, brown is "non-core" habitat designated by Washington Ecology.  Blue is non-core habitat designated by Washington Ecology that the USEPA felt should be designated core.  Green is core habitat for char where the WA and EPA agree.

The maps are nicely rendered PDFs.  The streams are rendered using vector graphics, which means you can zoom in as much as you need without pixellation.  There are one or two maps per "Water Resource Invetory Area", typically a "non core" map, and in WRIA's that support salmonid spawning, a "spawning map".  The very few WRIAs that don't support salmonids at all (in the east) don't have any maps.

To keep the download file size manageable, we packaged the maps in two zip archives: WRIA 1-20 in one archive, and WRIA 21-50 in the other.