Sounds like an awesome trip. If you don’t get anyone else to join ya’ll, be safe and have a great time! I found this little bit of info incase it may help.. from 8/11/09
"Checked out in the Marietta Landing area of Lake Murray this past weekend. Visibility on the platform was about 6ft and the water temperature hovered around 85 degrees-ish. I got by with swim trunks the first day and a shortie the 2nd day, since we went down below the thermal-cline. kind of boring, but at least this way my experiences can only get better!"