All Im gonna say is you got to hit it!
Ive some experience in river diving and if its dark the partner theory is nill. You cant see them or find them. Im guessing you are diving the river for goodies as I do. :O) So you dont need to be anywhere but the bottom. If the River doesnt have a lot of current... flips you over backwards with 40 around the waist then you good. Not sure abt the TN River but I know of a lot of artifacts from it!!! Since you dont have tidal shifts then go try it, make sure your inthe current. Less likely the reptiles in moving waters! Plus so far I have not been tested with one.
Ive dove about 5 of the Florida rivers and yes the water is dark, but once you are down the eyes focus in on the color. I use a UKD8 and so far Its been good. Remember when you cant see your mask a light aint worth a flip anyways! But stay in current, trees will tumble and the limbs will usually disappear and leave logs. Do not go into those places that look like eddys or jams. Wait till your ready.
I carry 4 knives and line cutters. Go over some cave diving tips and get rid of anything that will cause an entanglement. Fishing line will jack you up! We encounter old nets, fishing line, which if you pay attention will usually collect some sort of algae or debris on it and just stay away. Be careful arounf the banks. you can easily in low light go under a ledge and leave you in an overhead environment. So pay attention when you crawl around. If you have 4 knives you can probably get a hold of one! so another reason to be safe. Heading rocks is another thing that may happen to you cause you are looking down. So a perodic look is good, this will also let you know whats watching you!! :O)
You dont need a dive computer, and once you get in you will probably be a little hesitant about going in under trees and crap because its just dang spooky, and I dont care how many times you do it.. its freaking pucker time! But then again a 5 inch cumberland in the hand will make you brave!
I love to dive the rivers. Others like clear blue water diving with 50 ft viz..... I like it close so I can see each flake! Go little and try and get a buddy to go with ya, Id say a first timer alone isnt gonna be fun for ya. If someone is holding your hand its easier to go into the abiss!
Watch the banks check with boat ramp people and if there is a presence of gators just dont go where the big 10 footers are. Smaller wont bother you. :O) maybe! Remember moving water will suck the body heat off you faster too. So 70 degree water with that current might be cool, other than the same in calm or salt water. Wear a hood and have fun. Put out the flag. Know the laws and be smart. Make all gear entanglement free. HEY.. AND I DONT CARE HOW bad of a goober you look like I wear fins! Nothing like being on the other side the river and out of air and got 200 feet to swim back! BTDT!
FINS ARE YOUR FRIEND!
Steve