A zip line is a cable or rope stretched between two points of different heights, down which a person or materials can slide with the help of a suspended harness, pulley or handle.
The Upper Makefield Township Police Department said on Facebook on Sunday that "the flash flooding caught numerous motorists by surprise and many were trapped".
Nearly 150 people were still feared missing and many killed and as many as 14 bodies have been recovered after the tragic incident that took place on Sunday morning.
Uttarakhand Chief Minister Trivendra Singh Rawat said it is a matter of relief that the flow of the Alaknanda River beyond Nandprayag has become normal.