The UK's historic Privy Council is hearing a challenge to the construction of the 50-metre-high Chalillo dam in Belize, in central America. Our science correspondent has been to see the work in progress.
The long dirt road to Chalillo snaked up through the forests of the Maya Mountains in Belize and the potholes gouged by the tropical rain were so deep I wondered if our four-wheel-drive would make it.
The work is well advanced
Our first sight was a bleak encampment for the construction workers.
Row upon row of huts, surrounded by a sea of mud, house teams hired from as far afield as China, Nepal and India.
As we waited to be escorted to the dam site itself, the Chinese workers were preparing a feast to celebrate their New Year and their laughter rose above the gentle sounds of table tennis.
Two of the project's senior engineers led us further into the mountains, our cars eventually stopping on a sharp bend overlooking the deep valley of the Macal River.
Far below lay pale scars of bare earth where the jungle had been stripped to make way for access roads and assembly areas.
I hadn't realised how advanced the project was: heavy vehicles were in place along with a massive rock-crusher and two storage towers for cement.
Standing amid these giant works, it hardly seemed feasible that a panel of British judges, sitting on the Privy Council, could actually bring all this to a halt.
The dam's developers, the Belize Electricity Company, admit that the PR battle has hurt them - who could match a protesting Cameron Diaz in a canoe? - but they certainly believe that nothing will stop the project from being completed.
How it should look: Artist's impression of the dam (Image by Bacongo)
The case turns on whether the environmental assessment was adequately handled.
Campaigners argue that the rock at the dam site is sandstone not granite as the developers once claimed and that a fault-line running right over the site was conveniently removed from a key map.
The electricity company says its opponents latch on to the smallest error and blow it out of proportion.
Like so many projects of this kind, it's a question of balance between encouraging development and minimising destruction.
What will be lost? What will be gained?
Belize's image as an eco-friendly tourist destination may suffer if the dam goes ahead. On the other hand, asks a senior electricity executive, how will those tourists enjoy air-conditioning if we don't go ahead?
The dilemma is clear. The problem is the effects of the dam are likely to be irreversible.
During my stay, I was cooled by an electrically powered fan but also woke to a gentle orchestra of bird-song rising from the banks of a river that may be changed for ever.