The WWF says fewer than 80 dolphins are left ( Image courtesy WWF)
Pollution in the Mekong river has pushed freshwater dolphins in Cambodia and Laos to the brink of extinction, the conservation group WWF has said.
Only 64 to 76 Irrawaddy dolphins remain in the Mekong, it says, and calls for a cross-border plan to help the dolphins.
Toxic levels of pesticides, mercury and other pollutants have been found in more than 50 calves that have died since 2003.
The Mekong flows from China through Laos, Cambodia, Thailand and Vietnam.
"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," said WWF veterinary surgeon Verne Dove in a press statement.
The group said it was investigating how contamination had entered the Mekong river.
Since 2003, the dolphin population has suffered 88 deaths, of which more than 60% were calves under two weeks old, it said.
"Necropsy analysis identified a bacterial disease as the cause of the calf deaths," Dr Dove said in the WWF report.
"This disease would not be fatal unless the dolphin's immune systems were suppressed, as they were in these cases, by environmental contaminants," he said.
Researchers found toxic levels of pesticides such as DDT and environmental contaminants such as PCBs during analysis of the dead dolphin calves.
These pollutants may also pose a health risk to human populations living along the Mekong - who consume the same fish and water as the dolphins - the group suggested.
High levels of mercury were also found in some of the dead dolphins, which directly affects the immune system making the animals more susceptible to infectious disease.
"A trans-boundary preventative health programme is urgently needed to manage the disease affected animals in order to reduce the number of deaths each year," said Seng Teak, Country Director of WWF Cambodia.
The Mekong River Irrawaddy dolphin, which inhabits a 190 km (118 mile) stretch in Cambodia and Laos, has been listed as critically endangered since 2004, the WWF said.
The Irrawaddy dolphin is also seen in parts of South Asia.
There too it has dwindled in numbers, although last year thousands of Irrawaddy dolphins were found in Bangladeshi waters when they were previously thought to be extinct in the area.