A 250-square-foot rock slab broke from an alcove and capsized the couple's pontoon boat near Lake Canyon, about five miles downriver from Halls Crossing and Bullfrog.
Other boaters, who found the capsized vessel, told authorities they had passed the boat and waved to two people onboard about 20 minutes before the boat tipped over. The boaters contacted authorities about 3:15 p.m. Friday to report the accident.
Divers on Tuesday continued to search for the Donald Simmons. An underwater robot was also being used. Donald Simmons was an avid horseman who played guitar and sang at his church, while Mary enjoyed fishing, said Donald's older brother, Wesley.
"We're just hoping they can locate his body and get them both back here so there can be closure," Wesley Simmons said. "I just hope and pray he's not under that big rock," Wesley Simmons said.