I have only seen one in my total of 28 years in Tennessee. When a student at TWC, another student found one trapped in a hole in a rock when the generators shut down. Brought it to class and we kept it in a cooled tank for a couple of days, then he released it back on the Hiwassee.
FYI: the hellbender is Cryptobranchus alleganiensis; the mud puppy or waterdog is Necturus maculosus. They are two different salamanders. College prof. was real big on salamanders. Spent a lot of time in the outdoors for his class on mammalian zoology. I remember my grandfather telling about the poison bags on the neck of the water dog; turns out they are actually gills.