Where are the designated areas for swimming from a boat? Everything mentions this but the areas are not listed.

You can swim off the boat anywhere. Granted there is places in the lake where you can take your boat very fast and then there's places where you're not allowed to do that and that's where most people get out of the boat and swim.I really wouldn't overthink it you'll see exactly what's up when you get there it's nothing to stress on.

Is trailer camping possible

By the marina or by the dam are both good places, but as mentioned, just about everywhere and you will see as you drive around.

Beach

There is a sandbar by the old marina they call the "boater beach"

I'm not sure about that. You could call 740-432-1508 and ask