Actually, Santeetlah is closer to Fontana than Nantahala is (although they're all fairly close). Santeetlah is actually located in the town of Lake Santeetlah, but it's really just a small community just outside of Robbinsville. If you're coming towards Fontana from east of Fontana, you will take highway 28 North and then take highway 143 towards Robbinsville. This will put you in Robbinsville, so then take a right at the light to get on highway 129. After only a few miles you will see the lake, crossing it a few times. Where I usually dive at is the Cheoah Point rec. area - you will see a sign for a left turn to it and Joyce Kilmer Memorial Forest.
Nantahala Lake is located on highway 1310/Wayah Rd between Franklin and the Nantahala River Gorge. I dove nantahala once last summer and experienced almost complete loss of light around 40ft. Turns out my gauges were dragging the bottom as a descended, stirring up muck which I think blocked out all the light. I could be wrong though. Nantahala is a beautiful lake, but a couple of things about it. First, it is a boaters or homeowners lake. There is no recreation area, only three boat ramps. There is a sheer rock wall near the dam though, which might make an interesting dive (although it's so close to the restricted area I would only do it with a guide rope, if at all). Where I have dove is off the highway where the Bartram trail intersects. There's access to the lake that's usually not too heavily frequented. Also, the lake's elevation is around 3000ft (Santeetlah is around 1600ft). When I dove there last summer, the water temp was 80 at the surface and stayed around 80 until it dropped to 65 around 40ft.
I dove Santeetlah May 28th and the surface temp was 80 and around 30ft is was a chilly 55. I might be going back this weekend, and with several days in the 90s I'm hoping it has warmed up a bit. I'll let you know.
My LDS is in Asheville, so if this is your shop let me know and the next time I'm by we can discuss it more in person. Otherwise, I'm glad I can give you some helpful info which I will be more than happy to continue to help you out with in any way I can.