The World Wide Fund For Nature (WWF) has reported the death of an Irrawaddy river dolphin, believed to have been one of just six left in Laos.

River-dwelling cetaceans worldwide are in great danger. Between pollution, hunting and accidental kills from being hit by boats, they have disappeared entirely from the Yangtze and are in decline in most other places.

The Irrawaddy dolphin (Orcaella brevirostris) once lived in rivers and estuaries throughout much of southeast Asia, as well as in coastal marine environments. Most closely related to orcas, the dolphins grow to 2.3 meters (7.5 feet) in length. Their long gestation period, 14 months, makes it particularly hard for them to replenish lost populations.

Although the dolphins tend to prefer the brackish waters of estuaries, populations became established upstream in major rivers of the area, including the Ganges, Irrawaddy and Mekong. Only the Bangladesh population is thought to be close to healthy, with around 6,000 survivors.

The isolated Mekong population is teetering on the verge of extinction. The section of the great river that forms a boundary between Cambodia and Laos was once a population center for the dolphins, but numbers are thought to have fallen by around half over recent decades.

The WWF considers fishing methods such as gillnets and explosives to be the prime cause of the dolphins' decline. All of these are illegal on the Cambodian side of the border, where approximately 80 dolphins survive, but gillnets remain legal for the majority of the river sections under Lao control.

The final straw could be the construction of the Don Sahong Dam, 3 kilometers (2 miles) upstream of the main dolphin habitat.

The dolphins are of economic as well as ecological significance, drawing tens of thousands of tourists to the area. “The small population size and high calf mortality means these rare and beautiful dolphins are facing a highly uncertain future, but there is still hope for them. Joint conservation action between both countries is paramount,” said Teak Seng, WWF-Greater Mekong Conservation Director. “The key is collaboration between Laos and Cambodia. It’s time to end the use of all types of illegal fishing gear and strictly regulate the use of gillnets and boat traffic. Working on these issues is the only long-term hope for the dolphins' survival in Laos and the greater Mekong.”