• The Mekong River reverses its flow each year, turning Tonle Sap into a vital source of fish and nutrients for Cambodia’s farms and fisheries.
• Cambodia’s annual water festival, which celebrates this natural phenomenon, has been cancelled for the second year in a row due to national security concerns and the need to shelter displaced people.
• The cancellation of the festival has had a significant impact on Cambodia’s economy, with overseas visitor numbers falling by 48% in the first five months of 2026 compared to the same period last year.

The mighty Mekong River and the adjoining Tonle Sap river and lake system are the lifeblood of Cambodia's farming and fishing and near enough the country's heartbeat.

Each year, as the monsoon takes hold, the surging Mekong pushes into Tonle Sap, swelling what is already Southeast Asia's biggest lake. But when the monsoon ends and dry weather returns, the flow reverses in what is a phenomenon unseen anywhere else in the world as the lake fills the river with fish and sends nutrients downstream to adjoining farmlands and the rice-growing Mekong Delta.

Cambodians have long honoured the annual cycle with an annual water festival held in October or November - whenever the monsoon is deemed to have come to an end. The highlight of the event is a series of boat races for which competitors from across the country train for months and which are watched by tens of thousands of revellers sat on the sloped terraces and banks along the city's riverfront.

And in an economy where tourism makes up around 10% of gross domestic product, the water festival is an annual draw that brings in thousands of visitors as they make their way along the Indonchina backpacker trail.

But not this year - again. The Cambodian government has announced that for the second year in a row, the festival will not be staged, with national security concerns and the need to shelter displaced people cited as priorities needing to be addressed.

Since last year, the kingdom has been embroiled in border war with its much bigger and wealthier neighbour Thailand, a conflict that has seen thousands of people forced from their homes and the near-collapse of cross-border traffic and tourism.

Cambodia's overseas visitor numbers fell by 48% in the first five months of 2026 compared to the same period last year in a blow for the country's economy following significant investments in two new international airports aimed at bringing in more long-haul visitors to attractions such as Angkor Wat, a 12th Century Hindu-Buddhist temple complex in the north-west.