Divers with the Los Angeles County Sheriff's Department's Special Enforcement Bureau began searching for the men in the California Aqueduct on Saturday.
Grigor Khacheryan, 78, and Minas Khacheryan, 86, were last seen Friday morning on Chevy Chase Drive in Glendale. The siblings went to Lancaster to go fishing when they disappeared.
Grigor recently had open heart surgery. His older brother Minas has a heart condition and is missing his left eye.
Authorities say their family is concerned for their well-being and are asking for the public's help. Anyone with information about their whereabouts or about what happened to them are urged to call the sheriff's department at (323) 890-5500.