One river feeds the rice fields and fisheries of five countries. The decisions that determine how much water arrives are taken upstream, by whoever built first.
The Mekong supports one of the largest inland fisheries in the world and the
rice economy of the delta at its mouth. Its usefulness depends on a rhythm: a
flood season that pushes water backwards into Cambodia's great lake, and a dry
season that lets it drain again. Dams smooth that rhythm out. Smoothing it out
is precisely what they are built to do.
Upstream advantage
Hydropower is the most attractive export a mountainous, landlocked economy can
develop, and Laos has pursued it deliberately. China's cascade on the upper
river came earlier and is larger. Neither country is doing anything unusual;
states generally use the resources inside their borders. The difficulty is that
a river crosses borders and a reservoir does not.
The result is a familiar structure. The benefits of storage are national and
countable: megawatt-hours, export earnings. The costs are regional and diffuse.
A fish migration that fails. A sediment load that no longer reaches the delta.
A flood pulse that arrives late.
The delta is subsiding
Vietnam's delta provinces sit barely above sea level. They are losing ground in
two directions at once: sediment that used to rebuild the land is trapped behind
dams upstream, while groundwater extraction causes the surface itself to sink.
Salt water moves further inland each dry season, and rice gives way to shrimp
ponds in fields where it grew for generations.
Governance without enforcement
The river commission that coordinates the four lower-basin states can convene,
study and recommend. It cannot refuse a dam. Its membership does not include the
largest upstream builder. What exists is consultation; what would change
outcomes is a right of veto that no government has been willing to grant a
neighbour.
What to look for
The measurable signal is not the number of dams. It is the shape of the annual
flood: how high the peak, how long it lasts, how far the reverse flow into
Cambodia's lake reaches. Those figures describe the livelihood of tens of
millions of people more accurately than any national growth statistic in the
countries the river passes through.
