Eight black rhinoceroses died after being transported from a national park in Kenya to a sanctuary meant to help preserve their critically endangered species, the government said on Friday.

Wildlife workers say they believe the rhinos died from drinking water with a high saline level in their new environment while being accustomed to fresh water, according to a statement from Kenya’s Ministry of Tourism and Wildlife. The government did not specify when the rhinos had died, but said such a high death rate in this sort of transport was “unprecedented” in the country.

The death toll startled conservationists in Kenya who were already mourning the loss of the last male northern white rhino, which died there in March. Paula Kahumbu, the chief executive of WildlifeDirect, a conservation group in Kenya, called what happened to the black rhinos a “complete disaster.”

“Kenyans must demand an explanation and full transparency as well as reassurances that we will adopt the best practices in wildlife translocations to learn from this disaster and prevent it from ever happening again,” Ms. Kahumbu said in a Facebook post on Friday.