A reef south of Savary. It is called Mystery Reef because no one knows why it is called Mystery Reef.
1. According to the Thurber Report, Savary Island used to extend all the way to Mystery Reef:
"Storm wave attack over the past 11,000 years since deglaciation has reduced the Island from its former extent as far southeast as Mystery Reef. Storm waves and other natural processes continue to reduce the Island’s south shore."