The fish residing in Alaknanda river and its tributary Dhauliganga were observed to be behaving oddly before the flash floods on Sunday, reports TOI.

Around 9 am, the residents of Lasu village saw shoals of fishes close to the surface - so close that they could practically pick them up. Lasu is 70 km downstream from where the disaster struck an hour later.

“On any other day, it would not be possible to catch fish with bare hands. But there were so close, and so many, All of us brought back a lot of fish,” an observer was quoted as saying.

“Fish always swim in the middle of the stream. It was abnormal. They were only swimming along the edges,” said another.

They also noticed that the usually green water of the river had turned grey.

Similar behaviour of the fish was observed at Nandprayag, Langasu, Karnprayag, with innumerable mahseers, carps, snow trout swimming close to the surface near banks.

The reason behind this might be the subsurface vibrations that preceded the disaster. These vibrations could have damaged the sensors of the fish. The fish have a biological system, called the lateral line system, that helps them detect even minute changes in water movement and pressure.

“In this case, it’s possible that a sound preceding the flood may have been picked up by the fish. It is also possible that an electric wire or some electric source fell into the water and gave them electric shocks. There can be many reasons. This is why we say that dynamite blasting shouldn’t be done on a river,” a scientist was quoted as saying.