The absence of fishing boats on this stretch of the Mekong River, just a few kilometers north of the eastern Cambodian town of Kratie, means military policeman Em Pheap is doing his job.
One of about 80 "river guards," he is part of a groundbreaking conservation effort which has been credited with helping pull the Irrawaddy dolphin back from extinction.
"There, there!" he pointed excitedly during a recent patrol on the river, shouldering his assault rifle and standing high on the back of the boat.
The pair of dolphins, dark slivers on the horizon, broke the surface with a gentle exhale of breath heard over the murmur of the current running through the submerged trees in this vast monsoon season flood plain.
The total number of Mekong dolphins is unknown, but marine specialists say the mammals remain some of the world's most critically endangered.
With their pale gray skin and blunt beaks, the dolphins resemble porpoises more than their sea-going cousins.
Their numbers already vastly reduced by Cambodia's drawn-out civil conflict - dolphin blubber was used to lubricate machine parts and light lamps - these graceful creatures are now falling prey to development and the attendant problem of over-crowding as this wild corner of the country opens up.
The Mekong is one of only five freshwater habitats in the world for this species of dolphin, and Cambodia supports its largest remaining population, thought to hover around 100 congregating in natural deep-water pools.
"The Kratie-Stung Treng stretch of the Mekong is their last stronghold," said Richard Zanre, the World Wildlife Fund's (WWF) freshwater program manager in Cambodia, describing a river habitat running 200km from Kratie to Stung Treng, Cambodia's last large port before the Mekong crosses over into Laos.
War and the ensuing lawlessness kept the region largely out of the reach of researchers for decades. But since 2001, biologists and other wildlife experts have discovered an unexpectedly rich biosphere.
At its core are the dolphins, "a flagship species for the conservation of the river," says the WWF.
Desperate to revive a plummeting population, the government created the river guards, the first organization of its kind and part of a conservation effort launched last year after a spate of mysterious dolphin deaths.
But while the guards appear to have had some success in bringing dolphin numbers back up, they have been met with hostility and sometimes violence from local villagers who make their living along the river.
"The most important thing is to cooperate with the people," said Touch Seang Tana, chairman of the government's Commission for Mekong River Dolphin Conservation.
"Without the participation of the local people in conservation, we will not be successful."
A spike in deaths among dolphin calves last year left officials scrambling to re-think their conservation efforts as Cambodia prepared to launch one of its most ambitious tourism efforts to date: The Mekong River Discovery Trail.
The trail, which hopes to bring tourism and development to one of Cambodia's most neglected regions, roughly follows the dolphins' habitat.
The animals' survival is crucial to the plan's success, officials say.
"No dolphins means no tourism. No tourism means no development," Tourism Minister Thong Khon said last week as the trail, a joint UN-Cambodian project, was announced.
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