Viral infection caused the death of a 15-year-old female giraffe in the National Zoological Park here last week, Environment Minister Jairam Ramesh said on Monday.
Zoo authorities had last week indicated that contaminated water could be the reason for the herbivore's death.
Zoo officials have said "sudden occurrence of the viral infection" is the reason for the reason for the giraffe Anitha's death, Ramesh said.
Speaking to reporters after inspecting the work being carried out by the Municipal Corporation of Delhi (MCD) to clear the sewage channels connecting the Zoo, the minister said water contamination was the reasons for the recent death of black bucks as well.
"The first giraffe died because of freak accident. The black bucks died because of water contamination," Ramesh said.
In January, a young giraffe had choked to death in the zoo. Ramesh said the replenishment of clean water in the zoo will be done once in three days.
To end the problem of sewage water, channels from the zoo to the Millennium Park will be made operational by June end and the work of the channel within the zoo will be completed by November.
"It is a Rs 5.6 crore project. Full amount has been handed over to the MCD. Phase I work will be completed by the end of June this year. Phase II will be completed by the end of November," Ramesh said.
Meanwhile, zoo officials said black bucks will be moved from the areas where the zoo remains submerged during the monsoon.
The union environment minister also asked the zoo officials to make arrangements to bring zebras and cheetahs to the zoo.