How the delta works, and what is changing

A delta stays above water only if new sediment keeps arriving to replace what settles and erodes. According to figures from the Mekong River Commission reported in 2019, the river carried about 160 million tonnes of sediment a year on average before the first dam in 1990, and about 80 million tonnes by 2019. The same report projected a further halving if eleven large dams and more than a hundred tributary dams are built by 2040. Some research goes further: a model by a team led at UC Berkeley, cited in Vietnamese reporting in 2025, suggested dams could cut the sediment reaching the Tien and Hau rivers by up to 96%. That is a modelled scenario, not a measurement, and we present it as such.

Sand mining in the rivers, the same 2025 reporting notes, is another cause of bank and coastal erosion. On the coast, the result is visible: a 2022 report counted about 286 km of the delta's 744 km of coastline eroding or severely eroding.

Every dry season the river runs low and the sea pushes up the mouths. How far depends on how much water comes down from upstream, on the tides and on how the gates and canals are managed. The national forecasting centre publishes bulletins through the season. Its bulletin of 10 March 2026 forecast the peak for March and April and put salinity of 4 parts per thousand at:

The same bulletin rated the season below both 2024–25 and the multi-year average. The worst recent year was 2020: the agriculture ministry's review found 10 of 13 delta provinces affected, the 4 g/l line covering 24.5% of the region — more than 50,300 ha more than in 2016 — and salt arriving nearly three months early and lasting two to two and a half times longer than in the previous extreme year. The provinces most exposed are the coastal ones: in pre-2025 names, Long An, Tien Giang, Ben Tre, Tra Vinh, Soc Trang, Bac Lieu, Ca Mau and Kien Giang.

The delta covers about 12.8% of Vietnam's land and produces more than half of its rice, about 95% of its rice exports, 65% of its fruit exports and 60% of its seafood exports. Reporting in May 2026 noted that rice area is falling while fruit and aquaculture grow, and that the national programme for one million hectares of high-quality, low-emission rice by 2030 aims at quality and lower emissions rather than more land. On the coast, some rice fields have become brackish ponds. Upstream, high dykes allow more crops but trap sediment outside the fields. Every trip on this site looks at one part of that trade-off.

• Official or primary sources first: government bulletins, ministry reviews, provincial plans, peer-reviewed research, the national tourism authority
• Every figure carries its date. A salinity figure from 2026 and one from 2020 tell different stories
• Modelled projections are labelled as projections
• When sources disagree we say so, or we leave the number out
• When a newer official figure appears, we replace the old one and change the date

See these forces on the ground on Water and Salt (coast and salinity) or the Delta Study Programme (flood, dykes and fish). The Ben Tre coast and Chau Doc pages describe the places.