The Mekong River is a lifeline for millions in the six countries it traverses on its way from its headwaters to the sea, sustaining the world’s largest inland fishery and abundant rice paddies on Vietnam’s Mekong Delta.

Cambodia’s plan to build a massive canal linking the Mekong to a port on on its own coast on the Gulf of Thailand is raising alarm that the project could devastate the river’s natural flood systems, worsening droughts and depriving farmers on the delta of the nutrient-rich silt that has made Vietnam the world’s third-largest rice exporter.

Cambodia hopes that the $1.7 billion Funan Techo canal, being built with Chinese help, will support its ambition to export directly from factories along the Mekong without relying on Vietnam, connecting the capital Phnom Penh with Kep province on Cambodia’s southern coast.