Two other elephants avoided getting swept away but were trapped for a time when they tried to climb out of the rugged canyon.

There were no witnesses to the episode, but park officials said that the animals’ tracks at the scene and their typical behavior supported the belief that the adults were trying to help the calf and one another when they got caught in the current and were swept over the waterfall.

Park rangers were alerted to the disaster by the sound of the distraught survivors trumpeting in the early hours of Saturday morning.

A similar accident occurred in 1992, when eight elephants were swept over the same waterfall and died, said Edwin Wiek, founder of Wildlife Friends Foundation Thailand.

The 260-foot waterfall is known as Haew Narok, or Hell’s Abyss.

The national park, about 80 miles northeast of Bangkok, has installed fencing along the banks of the 115-foot-wide Samor Poon Creek to try to prevent such accidents. But it was not sufficient in this case, Mr. Kanchit said.