The bodies of five more wild elephants have been discovered below a steep waterfall in Khao Yai National Park in central Thailand, officials said on Tuesday, bringing to 11 the number believed to have been swept away over the weekend after a calf slipped and the others tried to save it.

Park officials discovered the additional bodies on Monday when they flew a drone over the waterfall, which descends 260 feet and is known as Hell’s Abyss, in a search for two elephants believed to have survived the disaster.

This is the worst such episode for the park’s wild elephants in recent memory. A similar disaster killed eight elephants in 1992.

The director of the national park, Kanchit Srinoppawan, said it appeared that the elephants had been crossing a swollen creek after heavy rains when a 3-year-old slipped and the others tried to rescue it.