Leng Sokha’s bloodshot eyes welled with tears as she squatted next to the frame of her grown children’s wooden home. Between sobs, the 46-year-old explained that her sons, Un Bun Thorng, 22, and Un Bun, 24, had left the house unfinished when they went to Thailand in April with their partners to find work in garment factories.

For generations, Sokha’s family has lived in Bak Preah village on the Sangkae River – which passes through Battambang province and connects to the Tonle Sap lake about 70 kilometres away – depending almost solely on catching fish for their food and income.

But with the water levels remaining low and the cycle of flooding upon which the local ecosystem depends disrupted due to years of drought, the fish stocks have been decimated, forcing Sokha’s sons – and many others – to move elsewhere for work, a new phenomenon for the close-knit community.

“The situation got worse and worse because there is no water. I miss my children,” Sokha said. “Without them, everything is gone.”

Bak Preah is one of five villages with a total of about 1,050 families along the Sangkae in Prey Chas commune in Battambang’s Ek Phnom district.

Commune chief Long Phon said about 95 per cent of the villagers’ livelihoods depended on fishing, but catches had been declining for years, with 2015 and 2016 the worst anyone had experienced.

The peak of the fishing season is usually from October to November, when the area floods, flushing fish out of the commune’s three protected fishery areas – but there was no such flooding in 2015, and this year was not proving to be any better.

There had been no rain from January to May and less than usual in June, and lots of rain was needed for the area to flood, Phon said.

Phon said the lack of fish was forcing people to migrate to Phnom Penh, Battambang town and across the border to Thailand to take jobs in the garment and construction sectors. The villagers cannot turn to farming because it is illegal in the surrounding flooded forest areas.

Last year, he asked his village chiefs to start tracking the migration numbers and report back to him.

In 2015, 100 people moved away, but so far this year, 750 people have left – mostly single people and almost half women. “We cannot ban them from leaving,” he said. “There’s no other choice for them here besides fishing because we cannot farm.”

In the good days, villagers would get an average of 20 kilograms of fish per day, and would collect up to 6,000 riel (about $1.50) per kilogram, Phon said.

Now, some fish species had disappeared entirely, he said.

Rum Hing, 38, from the commune’s Reng Tbal village, said people lived in a “constant struggle”. Lately, he had only been catching 1kg to 2kg of fish per day.

“I have to leave,” the father of two said. “I want to do it, too. But I have no idea of where to go and where to work.”

Chuong Sothea, director of Battambang’s fisheries department, said water levels were down all around the Tonle Sap, but officials used Prey Chas as the standardised point to measure the water levels every month as well as in the middle of the Tonle Sap.

According to his measurement from June, the water level stood at less than half a metre, but with recent rain, he said it was likely to have increased to 6 metres this month.

Water levels below 1.5 metres made breeding difficult for the fish, he said, but no environmental assessment had been conducted in the area to assess the real impact.

Moeun Tola, executive director of labour rights group Central, said poor Cambodians who migrated faced a higher risk of being exploited because most of them were uneducated and could not read nor write. They were vulnerable to fake job promises as they are desperate to find work.

“People are taking risks to survive,” he said. Villagers needed to make sure they had clear information on their working conditions and wages before accepting a job in an urban area, he said. Even if they didn’t request such information, employers were required to inform them.

However, local authorities should provide assistance and information for those seeking to migrate, Tola added. Penh Chamroeun, 31, and her husband migrated to Thailand to work as construction workers in April to be able to provide for their four children, who stayed at Bak Prea village with their grandparents.

But the couple ended up in a worse situation – they were cheated by brokers and didn’t receive any salary for their work for three months. “I was crying and missing my children,” she recalled of her time in Thailand. She said she wouldn’t leave them again, even if it meant having to endure more hardship.

Choup Saun, director of Battambang’s provincial environment department, said villages around the Tonle Sap lake were facing similar challenges to those in Prey Chas commune partly due to climate change.

Saun said the problem was being exacerbated in Prey Chas because several of the Sangkae’s tributaries were being blocked to provide water for communities upstream, while illegal fishing in protected areas was further reducing fish stocks.

He said that if fish stocks in even half the protected areas could be maintained, there should be enough to support the communities, though he still described their dependence on fishing as “risky”.

“Without fishing, they have nothing to do,” he said.

Local government officials and NGOs have been trying to provide other ways for villagers to sustain themselves in the long term. For example, in 2010, 43 tourism boats were introduced. “It helps 43 families and the families rotate,” Saun said.

“What we can do is preserve the area, but we don’t know how sustainable it will be.”

Back in Bak Prea, Sokha said her sons had sent her $50 since leaving for Thailand in April, but she had to pay $10 for the boat ride to go pick up the money.

She said it wasn’t enough and she wasn’t sure whether it was worth her sons risking their safety. “My children said if there is water this year, they will come back,” she said. “I want them to come back to fish even though it’s difficult.”

Phon, the chief of Prey Chas commune, said people were waiting to see whether the floods would come in October. If they do, some may return.

But if it doesn’t flood, the exodus will continue.