Now.

There are fears that the Mekong River, which has one of the richest ecosystems on Earth, is in crisis. The Mekong sustains more than 60 million lives as it travels through China and Southeast Asia. It's facing an onslaught of dam building, intensifying climate change, and sand dredging. Downstream communities living on the region's largest lake, the Ton Sap in Cambodia, are reporting a decline in fish stocks of more than 80 % over the past 20 years. Our Asia Pacific correspondent, Laura Bikker, is in Cambodia to ask if the mighty Mekong can be saved.

Mai lives in a world of water that was once renowned for an abundance of fish. But in recent years, he and thousands like him have been asking, where are they?

These.

Past few years, there's less and less water and fewer and fewer fish. Now we have children, and every morning, I need around five dollars to get them to school.

And.

These days, I have no income.

It has.

Taken four or five days, and that's all I get. I have no fish to sell.

Since the 1990s, some countries have the Mekong River as a potentially powerful energy resource. China has built 11 dams on the mainstream. Laos has two. Dozens more are planned. Experts who monitor water levels in the dams are worried.

Rainfall that typically would fall during the wet season is much lower than normal. But at the same time, upstream dams are restricting water during that wet season. Climate impacts and dam restrictions are changing the way that the mekong flows much for the worse.

Studies suggest river nutrients and fish are now struggling to make it downstream, and when they do, they're struggling to survive. Elsewhere, the mekong has other gifts to give: sand. 60 million tons of sand is dredged from the Mekong each year to help construct developing Southeast Asian cities. That's the equivalent of 950 Olympic size swimming pools. Twenty-five-year-old Kuntia was jailed for more than a year for organizing protests to protect the river.

When I see this, it makes me worry about the Mehkong's fate and its impact on the Cambodian people as a whole.

The Cambodian government has long been accused of profiting from plundering the country's natural resources, which it denies.

But Cambodia is not alone in its insatiable desire for sand. It is the world's most mine mineral. The problem here is they are dredging at an already fragile ecosystem that scientists fear is on the edge of irreversible collapse.

There's a call now for governments in this region to work together to monitor water levels and dam construction. The flow of the mighty mechong has not yet been stilled, but its fate now depends on the resilience of the people it supports and how far they're willing to go to defend it. Laura Bicker, BBC News, Cron Pen.