The report released Thursday said researchers had found toxic levels of pesticides such as DDT and environmental contaminants such as PCBs during the analysis of the dead dolphin calves.
"These pollutants are widely distributed in the environment and so the source of this pollution may involve several countries through which the Mekong River flows," the World Wide Fund for Nature said.
Since 2003, the population has suffered 88 deaths of which more than 60 percent were calves under two weeks old. The latest population is estimated between 64 and 76 members living in habitats along a 190-kilometer stretch of the Mekong River between Cambodia and Laos, the report said.
Vern Dove, an author of the report and veterinarian with WWF Cambodia said "Necropsy analysis identified a bacterial disease as the cause of the calf deaths. This disease would not be fatal unless the dolphin's immune systems were suppressed, as they were in these cases, by environmental contaminants."
But, Touch Seang Tana, chairman of Cambodia's Commission for Conversation and Development of the Mekong River Dolphins Eco-tourism Zone, said the "report was all lies," citing it was aimed at discrediting Cambodia and alerting donors to give more aid to the WWF.
He said no such pollutions have been found or he and other 10,000 families living along the stretch have died or become sick because of the water consumption on a daily basis.
He, however, acknowledged the deaths of the dolphins, but because of illegal fishing in early 2000, not because of pollutants as claimed by the WWF's report.
He estimated dolphins numbered at about 150 to 160 today, while there were only about 120 in 2000.
The Mekong River Irrawaddy dolphin has been listed as critically endangered on the IUCN Red List of Threatened Species since 2004.