I spent a couple summers recently sampling hellbenders in the Little river and the Hiwassee river, both rivers support populations of hellbenders.
The hiwassee is loaded with them. There are quite a few in little river as well but there numbers are not what they used to be, that goes for the whole state. Hellbenders are an indicator species, they require cool clean fast flowing water, habitat loss has significantly reduced their range.
I'm not sure what the conservation status is for them in TN but most states they are found in have them listed as near threatened to endangered. I know they are a protected species in TN.
Here is a picture of one from the little river.
They may look menacing but they are harmless and if you are lucky enough to encounter one while on the water make sure to leave them be.