As much as I'd like to get my science, as well as my politics, from someone who, for a living, reads words written by another and stands on marks made with masking tape, I learned back in the 1970's, when it was still "Global Cooling", that most shark attacks occur in three feet of water.
Of course, it wasn't a Hollywood dolly bird who taught me that, but a SCUBA instructor formerly with the U.S. Navy's UDT school, so consider my source.