Tonle Sap, Cambodia – During Cambodia’s monsoon season, rice farmer Sam Vongsay’s backyard fills with water and the plastic trash of his houseboat-dwelling neighbours as the Tonle Sap lake grows with floodwaters from the Mekong River.
But during the dry half of the year, which runs from December to May, Vongsay can hardly access a drop of lake water from his home in Chong Khneas, which is located about 220km (137 miles) north-west of the capital Phnom Penh.
The 40-year-old farmer lacks a viable well or the equipment to pump the lake’s water the 2km (1.2 miles) distance to his property, and blames farmers upstream for diverting much of the flow to irrigate their crops.
“The water is not enough to come downstream, because the other farmers upstream also block the water,” Vongsay told Al Jazeera.
In the past, Vongsay and his family could cultivate two seasons of rice, but sparse rainfall in recent years and inadequate water infrastructure have made it difficult to manage a single harvest. Vongsay said he tried to grow chilis last year to diversify his crop, but the plants withered and died.
“We don’t have enough water infrastructure,” he said. “If we had that, we would not just grow rice, we would grow rice and other vegetables three or four times per year.”
The farmers along Southeast Asia’s largest freshwater lake are facing a growing threat to their livelihoods as growing demand for land, droughts attributed to climate change and hydropower development sap up precious water supplies.
Since 2018, the volume of Tonle Sap has dipped below its historical average, according to a Mekong River Commission (MRC) report that examined water levels between November 2020 and May last year.
The lake experienced a severe drought in 2019, as did the Mekong River system that it relies upon, leaving a lasting impact on water levels. In January 2020, the lake’s volume was about 6,000 million cubic metres, a little over one-third of its average dry-season volume, according to the MRC.
Siem Reap rice farmer Van Ra, 44, told Al Jazeera weather had not improved since the 2019 drought, with unseasonal wind and rains last year unearthing seeds put into the ground during the dry season.
To cover the costs of renting his farmland and spraying fertilisers – which he needs to do more frequently due to irregular weather – Ra tried to plant rice twice last year.
“It was useless because I had almost nothing to harvest,” he said. “Doing it two times is impossible because there’s not enough water.”
Population growth and rising land prices have triggered a rush to clear forests in the area for homes and agricultural land, creating more demand for water from the lake and its tributaries.
The lake, whose seasonal flooding is connected to snowmelt from China’s Tibetan Autonomous Region and Yunnan province, is also susceptible to expanding hydropower dam development, which scientists have linked to unpredictable water levels on the Mekong.
While farmers have felt growing pressure on their livelihoods, Tonle Sap’s fishing industry, which produces an estimated 500,000 tons of fish annually, has also been reporting smaller catches, leading some fishers to turn to fish farms or agriculture.
Brian Eyler, author of the Last Days of the Mighty Mekong, told Al Jazeera that in addition to hydropower dams on the Mekong, smaller reservoirs created to meet farmers’ needs – often without official approval – were putting pressure on the lake.
“These reservoirs are effectively stealing water from surrounding communities and blocking critical fish migration pathways in the world’s largest inland fishery,” Eyler said.
Vongsay, the farmer near Tonle Sap, said the expansion of a canal along his property in 2019 that was supposed to help him and other farmers access more water from upstream had caused him to stop farming completely.
“We first agreed that it would be okay to dig the canal deeper, but we didn’t expect it to be so deep,” said Vongsay, explaining that he was unable to drive his rented tractor across the expanded canal to till his rice field.
Vongsay said he and his family were surviving off a side business making decorations for Buddhist holidays.
Chea Seila, a researcher for the US Agency for International Development’s Wonders of the Mekong project, told Al Jazeera the combined effects of climate change, deforestation and infrastructure development on Tonle Sap showed that authorities needed to gain a better understanding of the delicate nature of the water supply and develop solutions that took these factors into account.
“It is interconnected. When people use more water without saving and no restoration, there will be insufficient ground and surface water,” she said. “Even [if] we have sufficient irrigation infrastructure, we don’t have water from the [groundwater] spring as well as from rainfall. It is still difficult to get sufficient water for the whole year and [will be] in the future.”