Higher water and treacherous conditions around Vernal Falls slowed the search and led to predictions that it could be weeks before the bodies were found.
"There is so much water and so much churning and so much power behind that water that it would just be completely unsafe to insert divers into the water," park spokeswoman Kari Cobb said. "You wouldn't be able to see anything."
Cobb said dangerous conditions could exist until late summer, particularly because of the heavy winter snowpack that has filled Yosemite's streams.
The Los Angeles Times said rangers scaled back the search for the three missing Californians. About 30 people had been assigned to the search, but that number was reduced to 20 Thursday.
The missing hikers were identified Wednesday as Ramina Badal, 21, of Manteca; Hormiz David, 22, of Modesto; and Ninos Yacoub, 27, of Turlock. The Times said they were members of a church group visiting the park and apparently climbed over a guardrail into the rushing waters above the falls.