You need a buddy on the surface, connected with a rope. Always start downstream, and work your way up, so the silt isnt making it worse, and you can control your speed better. Black water diving is NOT for everyone. It takes time, and still not everyone can take the black, and if its cold, its even worse. A buddy on the bottom with you is no help, both are just in the others way, but you need the buddy on the surface. Start in the shallow, and work your way into deeper water, or if you go down in the middle of the river, use a anchor, and go down the anchor line. With black water diving, there is always a chance of getting tangled up in junk, and there is usually plenty of it. Everything you do, has to be slow and thought out. There is usually always a bit of light, so you can go slowly, while your eyes get adjusted to the light, then you have two hands to work with, not one holding a light and another trying to hold on to a rope.
Good luck, but slooooowly