KANPUR: Thousands of fishes of different species including 'Chilwa' and cat fish died in the lake of Kanpur zoo following dip in the level of dissolved oxygen in the lake water. The dead fishes were found floating on the water surface in the lake spread in an area of 10 hectares. This according to the zoo vets was for the first time that the fishes in the zoo lake had died. The fishes had died in such a large number that the foul smell emanating from it which had made it difficult for the zoo staff to cleanse the lake. The incident created flutter amongst the zoo authorities. They contacted the Kanpur district administration, Kanpur Nagar Nigam, Kanpur Development Authority and the UP pollution control board and apprised them about the mortality of the fishes. Soon the zoo vets started disinfecting the lake to prevent more mortality. The postmortem examination of the fishes revealed that they died due to extreme dip in the level of dissolved oxygen in the lake water. The Kanpur zoo authorities and the zoo vets blamed the nullah which overflew inside the zoo campus to be the cause of dip in the oxygen level in lake water. The sewage waste from this nullah got mixed with the lake water. The nullah is situated on the land of the forest department adjacent to the rear boundary wall of the zoo. Whenever the sewage water is not pumped and this water is not put in the sumpwell (situated on the land of the forest department), it overflows and enters inside the Kanpur zoo. According to the zoo vets, the sewage waste and the water are the source of pathogens which can spread deadly diseases in the wild animals kept in the zoo campus. The autopsy concluded that due to mixing of some kind of toxic from the sludge and the sewage waste from nullah into the zoo lake that the oxygen level went low. On Saturday at the time of the incident when the dead fishes were found floating on the water surface in lake, the nullah was overflowing inside the zoo. The zoo vets rushed to the spot and got potassium permanganate sprinked over the sewage water and the sludge to counter toxicity. This worried the zoo vets further who stated that all this could be risky for the lives of various animals housed here especially those protected under schedule-I of Wildlife Protection Act, 1972.