Probably more than you probably want to know:
Casselman River (sometimes called Little Youghiogheny) is typical of many creeks rising in Garrett County. The region's small valleys form geological catchments that fill up to the point of being swamps in the springtime. These are called glades. The glade springs make for some beautiful creeks and small rivers in the early springtime, and Casselman is one of the larger ones. Many glade springs are at or near depletion by mid to late summertime, and generally don't re-charge until snows and spring rains come again. As a result, the Casselman (and many Garrett streams) flows strong and clear in the spring and early summer, but becomes little more than a series of pools connected by a trickle come mid July. Many of these streams historically have been home to wild brook trout, but the habitat situation is fragile under ideal conditions. I've heard conflicting tales about whether the Casselman has any wild brookies in it, but since some of its tribs do, it probably does to, at least in good seasons.
Going back maybe two decades or more, it became something of a springtime destination for big stocked trout in a classic east coast mountain setting, largely by accident (in more ways than one, since it is by the town of Accident). The tale is that there was a problem at the Bear Creek trout hatchery / rearing station between Grantsville and Accident. Knowing the glade spring limitations of the Casselman's drainage, state biologists decided to put the trout from the hatchery, including a lot of fish in the 14 to 20 inch range, in the stream. The game plan was to leave them in the Casselman until the Bear Creek situation cleared up, and then, when the water level was much lower in the early summer, return with shocking equipment and return the trout to the hatchery.
As happens in Garrett County, word spread quickly and people showed up to fish for the unusually large stockers, including fairly substantial numbers of out-of-towners. Tourism is important to the Garrett County economy, so there was local support for continuing to operate the Casselman as Maryland's version of a Keystone Select stream. As far as I know, they've continued with the larger-than-average trout stockings ever since.
The thing about the Casselman and all those creeks that look great in the springtime is that you have to evaluate them based on what they look like at their worst: the summertime when flows are minimal and the dead of winter when cold and low water can combine to make it too cold even for trout. Fun fact for fishing nerds: Casselman is in the Mississippi catchment, west of the Eastern Continental Divide.
Note: A lot of the stuff I post like this is based on research that I've done myself. In this case, the source was my dad, who was good about overlooking "fishing legends" and instead was not shy about contacting biologists and fisheries managers to get more reliable information. He got tired of hearing tales about some mythic stream near a tackle shop that was full of trout, only to fish there and find a parking lot had ruined the spot 10 years previously and the shop owner had given up fishing even longer ago. In his final few years, he loved having access to biologist reports and lists of wild trout streams and such on the websites of the various states where he fished. I gotta say, it makes finding new spots easier.
