They were walking along a stream in northern Coahuila state Tuesday when a sudden surge of water swept them away, state authorities said.

An initial investigation suggests the water rose quickly because rain-collecting tanks in nearby hills overflowed, the civil protection department said.

One of the hikers was 65 and the rest were believed to be from 15 to 20 years of age.

Two dozen police, firefighters and other rescuers took more than a day to locate the remains of the hikers, who were found Wednesday.