Authorities told Atlanta TV station Fox 5 that rescue crews have been searching Lake Allatoona since Saturday, when the man fell into the water.
Authorities say Tommy Moore of Plainfield, Ind., was at the lake to attend a family reunion when he fell in.
Sgt. Mike Barr of the Georgia Department of Natural Resources says he was getting off a large boat to return to a dock and the boat separated from the dock.
Barr says there were about 20 people on the boat, and two of them jumped in immediately but weren't able to find Moore.