Six rare blind dolphins were found dead at the bank of the Indus River in Pakistan over last month, mainly due to low water level and contaminated water, local sources said Thursday.

Authorities responsible for wildlife conservation are carrying out investigations to determine the real cause behind the killing of blind dolphin. They said that water levels are very low in the Indus River now due to which a small amount of poisonous chemicals can kill a large number of fish.

Initially, fishermen of the area have been alleged as using poisonous chemicals to catch fish, which contaminated the river water.

Talking to Xinhua, Meer Ali, an elderly fisherman said that he and his fellow fishermen used chemical in a very small amount which neither contaminated the water nor harmed fish.

"The chemical which we use to catch the fish makes them hover over the surface of river, it does not kill them," Ali said.

Khalid Khan, a fisher man of 28, accused the toxic waste released as the reason of the killing of fish in the Indus River.

"Poisonous release of factories from southern Punjab is the real culprit as a large amount of poisonous waste from the factories pollutes the rivers, which are tributaries of the Indus River," Khan said.

Blind dolphin is a rare breed of dolphin which is found only in the Indus River of Pakistan and it has been declared the second most threatened fresh water dolphin species by the World Wildlife Foundation (WWF). A 2006 survey report said the number of this mammal is only 1,300 in the river.