By Guy Delauney
BBC News, Kratie
Sun Mao leans forward in the boat, shades his eyes with his hand, and squints across the wide expanse of the Mekong River where it twists through the town of Kratie.
Sun Mao has been trying to stop the dolphin decline
He is looking for one of the world's rarest mammals - the Mekong Irrawaddy dolphin.
Older people in this part of northern Cambodia talk of how they used to take the dolphins for granted.
Little effort was needed to see them in their dozens. Now, scientists say, there are less than 100 remaining.
With a practised eye, Sun Mao spots a group of five dolphins, collectively known as a pod.
They briefly break the surface as they come up for air - grey-brown, bullet-headed and exhaling with an old man's rasp.
It is an awe-inspiring sight, but nothing new to Sun Mao.
As part of a local organisation, the Cambodian Rural Development Team (CRDT), he has put years of work into preserving the dwindling population.
For him it is an issue of national heritage.
"This is the last place for these dolphins in the world," he says over the clatter of the boat's outboard engine.
"We have to conserve and keep them alive in this river for our next generation."
CRDT has tried to educate the local human population about what they can do.
A government-enforced ban on the use of gill nets - nets set vertically in the water so that fish swim into them and are entangled in the mesh - has cut down the number of dolphins accidentally caught by fishermen.
Instead, CRDT has helped locals to reduce their reliance on fishing by offering alternatives such as poultry farming.
Villagers on Pdao Island, just outside Kratie, greet Sun Mao as an old friend as he clambers up the muddy riverbank.
They happily show off their CRDT-sponsored chickens, water-pumps and fish ponds, and declare themselves delighted to be part of the dolphin preservation efforts.
It would be a heart-warming tale, if only the statistics were not so brutally depressing.
Local people would benefit from tourism if dolphin numbers rose
A scientific survey taken three years ago estimated the dolphin population at 127. The latest study by the World Wildlife Fund (WWF) puts the figure at 71.
It comes as a devastating blow after all the work that local and international organisations have put in.
As well as banning the use of gill nets, the government has established a network of river guards to patrol the dolphin habitats.
While CRDT has been working with the local human population, WWF scientists have been looking into ways of protecting the dolphins.
Everyone was hoping that the dolphin population would at least stabilise, if not flourish.
Payback would come in the form of an influx of tourists to see the pods at play and bring much-needed revenue to the local economy.
That dream recedes as each dead dolphin washes up on the banks of the Mekong.
Most worryingly, most of the recent casualties have been calves. Without the babies, there is no future for the species.
"There are theories that the immune systems of the dolphins have been compromised by stress," says Richard Zanre, dolphin programme manager for WWF.
"The river environment has been encroached upon by new developments. There is also the problem of contaminants in the river."
The answers need to be found quickly. As it stands, WWF still classifies the remaining population as "sustainable".
If the numbers fall much further, however, there will no longer be enough diversity for the dolphins to breed successfully.
That would spell the end for this unique species.