Why don't we build big dams anymore?

A dam is not a wall with a pretty lake. It is geology, people, downstream countries, permits and a decade of concrete. Ethiopia, China and the West each hit a different wall.

Oct 03, 2026

TL;DR

The West mostly stopped building big new dams on main rivers. The best sites are already dammed, and fish, water rights, safety rules and cost now decide more than the concrete does.
Ethiopia finished Africa’s largest hydropower dam, the 5,150 MW Grand Ethiopian Renaissance Dam, in September 2025 for about $5 billion. There is still no binding deal with Egypt and Sudan on how it runs.
China is building the biggest hydropower project ever: a planned 60 GW cascade on the Yarlung Tsangpo in Tibet, started in July 2025, costing about 1.2 trillion yuan, in earthquake country upstream of India and Bangladesh.
California’s Sites Reservoir, first proposed in the 1950s, would be the state’s first major new reservoir since 1979. Its water right is still up for a vote on 4 November 2026.
Just rebuilding an old dam for earthquakes now costs billions. Anderson Dam in California is about $2.8 billion and runs to around 2034.

Listen up.

Short answer first: in the West we mostly don’t, because the good sites are taken and the river already has owners. Fish, farms, cities, tribes, downstream neighbours and safety regulators all have a say, and the permits can take longer than the pour. China and Ethiopia still build giant dams. They hit the same walls. They just decided to push through them.

People talk about a new dam like it is a swimming pool with a plug. It is a wall across a living river, or a new lake off to the side, plus tunnels, turbines, roads and a fight about who owns the water.

Engineers did not forget how to pour concrete. The river already has a queue.

What does a dam actually have to do?

A dam has to:

Sit on rock that will not slide. The foundation and the valley walls (the abutments) carry the whole push of the lake.
Hold a lake that will not leak through cracks in the rock around it.
Survive the worst flood it could ever see, and in many places a serious earthquake.
Let enough water through that people and farms below it do not go dry.
Last a century while silt from upstream slowly fills the lake.

Miss one and you do not have a power station. You have a liability.

Ethiopia: the dam got built, the fight did not end

The Grand Ethiopian Renaissance Dam (GERD) on the Blue Nile is Africa’s largest hydropower plant: 5,150 MW, with a reservoir of about 74 billion cubic metres. It cost about $5 billion. Ethiopia paid for most of it itself, from government funds and bonds sold to its own citizens, with some Chinese loans. It was inaugurated on 9 September 2025, about 14 years after construction began.

That is the engineering win. A poor country finished a giant concrete job.

The hard part in 2026 is not the pour. It is the river below. Egypt gets almost all its fresh water from the Nile and calls the dam an existential threat. Sudan sits in between, with its own dams and its capital downstream. A 2015 Declaration of Principles was signed, but there is still no binding agreement on how Ethiopia fills and runs the reservoir in a drought. Egypt has taken the argument to the UN Security Council.

Lesson: you can finish the wall and still not be “done”. Downstream countries can fight you for a decade after the ribbon.

China: still building giants, in harder places

China already runs the biggest dams on Earth. Three Gorges on the Yangtze, 22.5 GW, is the famous one. Baihetan on the Jinsha, 16 GW, is the world’s second-largest hydropower station. It has been fully running since 2022, sending power east on ultra-high-voltage lines.

Now China has started the next leap. On 19 July 2025, work began on the Medog (Motuo) hydropower project on the lower Yarlung Tsangpo in Tibet, the river that becomes the Brahmaputra in India. The plan:

Five power stations in a cascade, about 60 GW in total, nearly three Three Gorges
About 1.2 trillion yuan, roughly $167 billion
The river drops about 2,000 metres in around 50 km through the “Great Bend”, so most of the water goes through long tunnels bored through the mountains rather than behind one giant wall
First power aimed at the early 2030s

It sits in one of the steepest, most earthquake-prone gorges on Earth, where the Indian and Eurasian plates meet. India and Bangladesh, downstream, have both raised water-security concerns. India is planning its own large dam on the same river, partly as a buffer.

China can still build at a scale the West will not match. That does not delete geology, resettlement or neighbours. It means China accepted those fights and kept the batching plant running.

The West: new dams are rare, and paperwork is the wall

Europe and the US largely stopped building big new dams on main rivers decades ago. The best sites were already taken, and fish, tribes, farms and “who pays when it goes wrong” won the argument. Much of the Western money now goes into fixing old dams, or removing them. The four Klamath River dams on the California–Oregon border came down in 2023–24, the largest dam removal in history.

California shows the honest 2026 picture.

Sites Reservoir is a new lake off to the side of the Sacramento River, not a plug in it. In wet years, water would be pumped from the river into a valley about 14 miles away and stored there: about 1.5 million acre-feet, roughly 1.85 billion cubic metres. Cost: about $6 billion. It would be California’s first major new reservoir since New Melones in 1979.

It was first proposed in the 1950s. In 2026 the fight is still the water right, meaning how much it may take from the river and when. The State Water Board issued a draft permit in March 2026. The project’s backers said the limits were too tight to justify the cost. A revised draft in September allows up to 986,000 acre-feet a year in high flows, and the board votes on 4 November 2026. If it passes, groundbreaking could come in 2027, with water around 2034.

Anderson Dam, south of San Jose, is not even a new dam. It is an existing earth dam being rebuilt because it sits close to active faults and could fail in a big earthquake. The reservoir has been kept low for years. A $1.88 billion construction contract was awarded in July 2026, the total project is about $2.8 billion, and construction runs from 2027 to around 2034.

That is what “just bring the old dam up to code” costs now.

In the West, the concrete is often the easy bit. The water right, the environmental study, the court case and the bill are the dam.

What constraints show up everywhere?

Rock and shaking. A wall in a gorge or a seismic zone is not a spreadsheet. The foundation decides the design.
People. Someone lives where the lake will be. Three Gorges moved about 1.3 million people. Move them fairly, or don’t build.
Silt. Rivers carry dirt. A reservoir is a giant settling tank, so it slowly fills up. Design for sediment or the lake dies young.
Downstream water. Farmers, cities and whole countries below you have a vote, even if it is only a diplomatic one.
Permits and money. A decade of studies can take as much attention as the pour. Cement, steel and labour are not cheap in 2026 either.
Time. GERD took about 14 years to build. Sites has been an idea for longer than most engineers working on it have been alive.

Same family as grid interconnection and hydrogen pipes. The map is easy. The kit and the neighbours are not.

Uncle’s verdict

Ethiopia: built the giant dam. Still arguing about the Nile.

China: still builds giants. Now in a seismic canyon with India downstream.

The West: mostly rebuilds and files paperwork. A new lake takes a generation of permits.

You don’t announce “we’ll just dam it” and then wonder why the river already had a queue.

— Engineering Uncle