Story highlights Police: Floodgates at hydroelectric plant's reservoir opened without warning

Students were taking photographs at the side of the river at the time

Three bodies have been recovered from the river so far

More than 20 Indian college students and their coordinator were swept away after a dam opened its floodgates apparently without warning and sent water surging down a Himalayan valley.

Rescuers have so far recovered only three bodies from the fast-moving river in the Mandi district of Indian's northern Himachal Pradesh state, police spokesman Kuldeep Singh Rana told CNN.

Emergency crews with divers and rafters were at the scene Monday trying to locate the remaining students, Rana said, though he warned the steep, rugged terrain of the valley was making the search operation challenging.

The incident took place at around 6.30 p.m. local time on Sunday when the group from an engineering college in southern India pulled over to take photographs along the Beas river.

All of a sudden, huge volumes of water hurtled downstream after being released from a reservoir at a local hydroelectric power plant, police said.

"Apparently there was no prior notice about the release (of water) from the dam. But an inquiry is being conducted," Rana said.

Local residents in the area staged protests in the aftermath of the incident.