Maryland published its first, state-wide water quality classification based on "designated uses" in 2010.  Of particular interest to us, cold water streams which are "suitable for the growth and propagation of trout" are classified as Class III or III-P.  III-P means the water is suitable for public drinking supply, so is the higher designation. 

The state DEP published a series of county maps showing the water quality designations across all of Maryland. III and III-P are shown as green lines (III-P are green dashed with black).

We've taken these maps and created a series of image overlays for Google Earth from them.  If you open the KMZ file for the appropriate county, it will load on top of the standard Google Earth imagery, and scale as you zoom in and out.  This makes them extremely useful, as you can see in the image of Allegany County shown below  (the original map is shown in the second image).  Once you find a stream of interest, you can turn off the layer (just uncheck its box in "My Places") and work in Google Earth.

An image of the original map is shown below.  Without the overlay, these maps aren't particularly convenient to use (the streams are not labelled).  But if you're not a Google Earth user (a mistake, IMO) you may find them useful. 11 counties have appropriate habitat.  You can download the complete set of KMZ files (a 6.6 MB download) as well as the individual PDF maps from the "MD Water Quality DU Maps" menu in the sidebar.