Do you want to buy a boat?” At the time, it seemed unlikely that this simple suggestion, made in a Phnom Penh coffee shop last year at a table full of friends, would end up changing the course of my professional and personal life.

But in late 2014, a few colleagues and I were looking to step back from the frantic pace of news gathering, slow down and gain more authentic insight into a topic. And the best way to do that, we decided, was to get a boat.

South African photographer Gareth Bright and I bought a retired wooden fishing boat in Pursat province and spent nearly a month steering it from Phnom Penh towards Siem Reap, producing stories along the way. This unorthodox approach to “slow journalism” attracted the attention of the international clean water organisation Lien AID, who offered to fund a much bigger project: the entirety of the Mekong river.

Along with videographer Pablo Chavanel, who joined the project to add a multimedia element, we have since travelled through Vietnam, Cambodia and Laos, documenting the Mekong’s people and the environmental challenges facing the river. China, Thailand and Myanmar are still to come, but what we’ve discovered so far is troubling. The Mekong, the world’s second most biodiverse river and the source of life for nearly 70 million Southeast Asians, is in real trouble.

In Cambodia, we found communities who had lived for generations on the river being forced to consider abandoning their way of life.

The Tonle Sap, translated as the “Great Lake” and often referred to as “Cambodia’s beating heart”, is the largest freshwater body in the region and one of the world’s most productive freshwater fisheries. It’s so productive, in fact, that the estimated quantity of fish caught in the Tonle Sap each year is greater than the entire recreational and commercial freshwater fishing industries of both Canada and the US combined.

The fish from the lake constitute the primary source of protein for the majority of Cambodians. As Taber Hand, founder of the non-profit organisation Wetlands Work! said of the Tonle Sap, “it’s a food factory – and you don’t have to pay to plant the fish”.

Yet when we headed to the floating communities of the great lake, where we spent nearly a week with local fishermen, we learned that this incredible resource was being strained to its limit. On one fishing trip we joined, we were told sharply to turn off our portable headlights because the boat’s captain had driven into a fish conservation area to cast his nets.

“Outside the conservation area there are no fish, so what should I do?” the captain responded when we asked why it was necessary to fish in restricted zones. “I am catching around 30 to 50 per cent less fish than I did [10 years ago], so we have no choice but to fish [here]. We know this is not good, and we are all worried about what will happen if there are no fish left [in the conservation area], but how else can we survive?”

Returning to Phnom Penh, we focused our attention on the community of Cham boat people living on the Chroy Changvar peninsula. We thought we knew this community well, having visited multiple times in the past, and assumed, perhaps naively, that, as boat-dwellers, the Chams would have a special love for the river on which they spent the majority of their lives.

Yet when we asked Yu Sos, one of the community’s political representatives, his response was stark and to the point: “No one wants to live on these boats. When it storms, we worry about our kids drowning, and they can’t go to school because we need them to help us fish. We are always fighting with land developers who want to have us evicted. Many of us can’t afford to buy water, and so we drink it from the river, which makes us sick – I have problems with my kidneys because of it.”

Sos went on to tell us that if given the chance, he would take his family and gladly leave the river behind forever if given the opportunity.

Following the Mekong north out of the capital, we next made our way towards the area surrounding Steung Treng to investigate what is possibly Cambodia’s most controversial environmental issue – the Sesan II hydropower dam.

When completed, the Chinese state-owned dam will block two of the nation’s most important Mekong tributaries – the Sesan and Sekong rivers.

The ensuing damages will be varied and devastating. Migrating fish will be unable to reach their breeding grounds; reduced sediment flow will disrupt the fertility of downriver farmland as well as increase erosion; a vast reservoir will displace thousands and inundate huge swaths of some of Cambodia’s only remaining healthy forest.

In the path of the proposed reservoir is the village of Kbal Romeas, home to 136 families of ethnic Phnong tribespeople, all of whom are facing the prospect of forced relocation. The question of whether or not to accept the compensation packages offered by the dam’s developer, Sinohydro, has divided the community. Some, especially among the village’s poorest or recently widowed residents, have accepted Sinohydro’s offer and are prepared to vacate their ancestral land, while others remain adamant in their opposition.

“There are three reasons I am against the dam,” 29-year-old Dam Samnang, a Kbal Romeas resident, told us. “It provides no direct benefits to people in this community; it will destroy all our houses; and it will ruin the river system so that we can never come back.”

Other countries we visited revealed similarly dispiriting but varied stories, showing how numerous and complex the threats facing the Mekong are, from the poisoning of parts of the Mekong delta caused by widespread dumping of agricultural chemicals into the water table, to the ecologically devastating damming of some of the Mekong’s most important tributaries as Laos tries to transform itself into the battery of Southeast Asia.

If the Mekong, one of the most bio-diverse rivers in the world and the source of life for tens of millions of people, is to survive in any meaningful way, great care must be taken to curb the severity of the damage being inflicted on it.

It’s a resilient river, and if given the chance it will continue to thrive and provide for those who live along its banks. But as Hand said of the Tonle Sap: “It is the human side of the equation, the human priorities, that don’t fit. We could have our cake and eat it too. [The solution] is right there for us to act on, but people want to work for themselves instead of together.”