The geographic data which is available for download on this site for free must have originally cost $100's of millions to assemble -- possibly $billions.  While some of it might have been gathered for other reasons, water quality regulation and management - i.e. complying with the Clean Water Act - are no doubt responsible for the presence of detailed stream databases in most of the states we cover.

Even more fortunate for us, Trout are treated by the clean water community much like the "canary in the coal mine".  When water quality degrades, trout stop reproducing.  So, built into the water regulations are often some specific indications of where trout might reproduce.  In some states this is implicit, but in other states trout reproduction is clearly indicated in the datasets.

This is because, in the middle of the last decade, the Federal Government changed water regulations to encourage classifying water by "designated use".  The idea is to identify how the water should be used, and then establish management criteria consistent with this use.  In many states, "trout propagation and growth" (i.e. wild trout), or some variation, is the key designated use for cold waters.  These data are essentially all new since the original WildTroutStreams.com website was created. 

Having said all of this, it also puts trout designation into a political realm.  Witness West Virginia where a major battle is going on right now over the definition of a Trout Stream.

One of our current projects has been to systematically search for and publish water quality data for every state we cover. 

To access, go to the "Streams" page for the state of interest.  There you'll find a "[STATE] Resources" menu in the sidebar which will take you additional web pages about the state, as well as download links to the data itself.