PAGE, Ariz. — The search will continue today for a man missing and presumed drowned at Lake Powell.

The National Park Service said Donald Simmons, 64, of Calhan, Colo., is still missing after a 250-square-foot slab of rock fell from an alcove onto a boat, capsizing it. The accident also killed his wife, Mary Simmons, 59.

"The search is hampered by poor visibility, the presence of trees underwater and the water depth is estimated at 150 feet," Marianne Karraker, a spokeswoman for the Glen Canyon National Recreation Area, said in a statement.