While the top of the dam is at 594 feet above sea level, the original 1914 design drawings called for the crest elevation (the highest water) to be 606.3. In 1997 the crest elevation of the dam's embankment was raised to 609.5 ft. so that the spillway could pass the probable maximum flood without the dam's embankments being overtopped.
The lake has never come anywhere near the 609.5 level. According to some records, the highest crest was in 1990 when the lake reached 598.7.
Here are the "official" lake levels:
594 - Normal Pool (full to the top of the dam)
597 - Minor Flood Stage
598 - Moderate Flood Stage
598.7 - Recorded high (1990)
Here are some historic high levels:
1990 598.7 - flood stage
2004 597.8 - flood stage
2007 596.1 - 11" under flood stage
At the 596 level, many docks are underwater and some of the homes on the lake are near to getting water in them.
If you live on the lake or are considering a purchase, you should understand the possible implications of high water. It's not a matter of "if" but "when."
(Photo by Angie Myrick Thomas 2015)