For a fisherman, the answer seems simple enough:  "If there are wild trout to be caught, it's a trout stream." Fair enough.

For the professionals that create the data we publish here, it's not quite so simple, because it's a question they may have to answer in the face of opposition from powerful political and economic interests.

The fisheries manager has to consider whether folks who show up to fish a listed stream are likely to have a reasonable experience.  So they have a bias to only show the "better streams".

For a water quality manager, paradoxically, a listed trout stream doesn't necessarily hold trout at all.  For them, trout are an indication that the water is of especially high quality that needs to be protected.  If there are wild trout in a "3rd order" stream (i.e. a stream that possesses two levels of tributaries to the ultimate headwaters), under water quality regulations, the 1st and 2nd order streams in the watershed will also be classified as trout streams, even if they don't hold trout.  If you think about it, it makes sense.  You wouldn't want people dumping warm water into a 1st order stream, even if devoid of trout, because it could devastate the second and third order streams into which it flows.

As a result, all listed trout streams generally carry significant restrictions on what landowners can do with the land that borders the stream, what they can dump in the stream, and how the watershed can be developed.  These restrictions are often viewed by landowners as "anti-development".  So a new listing can trigger howls of protest, often from very powerful interests.

As a fisherman, looking at this data, trying to figure out where to fish, it's important to understand these dynamics.  In practice, they affect how you interpret the data in a couple of important ways.

First, recognize that there's a built in bias NOT to list high order streams as trout streams.  This is true for both fisheries and water quality managers, for different reasons.  But the bottom line is that if there's a local stream that you think might hold trout, but it's not listed, by all means check it out.

Second, once a high order stream is listed, there's a legal necessity (if you're a WQ specialist) to list all of the streams in the watershed.  For the angler interpreting the data, it's almost certain that a listed high-order stream holds trout, but it's likely that some if not many of the headwaters stream may not.