Prominent Kenyan conservationist Paula Kahumbu said officials must take responsibility and should have explained what went wrong sooner.
The relocation of endangered animals, known as translocation, involves putting them to sleep for the journey and then reviving them.
The eight dead rhinos were among 11 that were moved last month to Tsavo East National Park, where wildlife officials hoped they would start a new population.
"Rhinos have died, we have to say it openly when it happens, not a week later or a month later".
The eight were among 14 black rhinos, eight from Nairobi National Park and six from Lake Nakuru National Park, which were transported in June in an operation announced by Kenyan Tourism and Wildlife Minister Najib Balala, who has yet to comment on the outcome.
The death toll while moving from the capital to a national park hundreds of kilometres away has been labelled "unprecedented" by the government.
"Moving rhinos is complicated, akin to moving gold bullion, it requires extremely careful planning and security due to the value of these rare animals", she said in a statement. One nonprofit, African Parks, has shipped several endangered species across the continent, including black rhinos, which it has flown from South Africa to Rwanda and Chad.
In a statement, Kenya's Ministry of Tourism and Wildlife, said, "Preliminary investigations by KWS veterinary teams attribute the deaths to salt poisoning as a result of taking water of high salinity on arrival in the new environment".
'Rhino translocations also have major welfare considerations and I dread to think of the suffering that these poor animals endured before they died'.
Kenya had a rhino population of 1,258 in 2017 of which 745 are black rhinos, 510 are southern white rhinos and three were northern white rhinos, having grown from less than 400 rhinos in the 1980s.
The relocation was part of the broader plan in partnership with Wild Wide Fund for Nature-Kenya (WWF-K) to create more secure space with suitable habitat for the rhinos.
According to KWS figures, nine rhinos were killed in Kenya a year ago.
In May, three black rhinos were killed in Kenya's Meru National Park.
The decline was caused by escalating illegal poaching for illegal markets in the Middle East and Asia.