Over the past three years, I’ve made repeated visits to the lake to chart how people are coping with these changes. The dozens of fishers I’ve spoken with all say the same thing: The fish are smaller, the catch is dropping, and no one is sure if the lake will make it. I met families whose daughters left home for factory jobs in Phnom Penh, and whose sons sneaked into Thailand for plantation labor. I met people who said they had to fish near protected areas, or use nets with tiny holes, or set traps with sticks from the forest, because if they didn’t resort to some form of illegal fishing, they would die. Nearly everyone I met was deep in debt.

“We’re river people,” Ly Heng told me the second time I visited him, in 2017. “When the water is low it affects us. Fishermen catch fish. If the water is low and they can’t — what happens?”

Mekong governments have long insisted that hydropower was necessary to provide electricity to their rapidly developing economies. On the upper Mekong, or Lancang, as it is known in China, megadams dot the river and its tributaries, delivering electricity but blocking sediment and, increasingly during drought years, water from moving downstream. On the lower Mekong, which runs through Myanmar, Laos, Thailand, Cambodia and Vietnam, each nation has embarked on its own dam-building frenzy.

Cambodia’s Lower Sesan 2 dam, located on a critical Mekong tributary, went online last year despite widespread opposition. (The drought was so protracted, of course, that the dam was rendered useless and power cuts roiled the country’s biggest cities for months.) Eleven more dams are planned or in construction for the mainstem of the lower Mekong, and 120 for the tributaries. Should all those dams be built, by 2040 the fish catch will drop by as much as half. While the economic gains of electricity could top $160 billion for the region, the loss of “natural capital” like forests, wetlands and wild fish could cost $145 billion. That drop in the fisheries could come at a price of nearly $23 billion.

Mekong governments can yet turn the tide. The cost of solar and wind power is plummeting. Some researchers believe that within just a few years it won’t make economic sense for investors to put money into hydropower. Others have suggested floating solar panels and micro-hydro dams as alternatives. A decade ago, Vietnam urged a moratorium on building Mekong dams until their impact could be studied. Instead, its upstream neighbors plowed ahead, and the impact is being witnessed in real time. If the Mekong’s role as an ecosystem isn’t given more value, the region will suffer shocks to food security and economic stability — drivers of conflict.

Time is quickly running out. In 2016, the drought brought wildfires to the forests surrounding the Tonle Sap, razing hundreds of thousands of acres of wetlands .

“Since my ancestors were here, since the gods of my father, during the dry season it’s dry in the Tonle Sap. If the water changes following the season it’s fine, but last year it didn’t follow the season,” Heng told me in 2017. “It was the lowest I’ve seen since I was born.”