The UK's Privy Council has dismissed attempts by environmentalists to block construction of a controversial dam project in the jungles of Belize.
The committee, the highest appeal court for the central American Commonwealth country, did not accept the Chalillo dam would threaten rare species.
The dam's backers say it is the most economic option for Belize, and will lessen its reliance on Mexican energy.
Two out of the five judges hearing the case disagreed with the council ruling.
The challenge over the 50-metre (165-foot) high Chalillo dam was brought by the Belize Association of Non-governmental Organisations (Bacongo).
They claimed its approval was unlawful due to inadequate assessment of the environmental impact and mistakes about the rock on which it will be built.
They believe its power output will not be worthwhile and say Belize's energy demands can be met in other ways.
It asked the council to overturn the Belizean government's approval of the dam, and order studies of its safety and impacts, with construction halted in the meantime.
Functions of the Privy Council - one of the oldest parts of the
British Government machine - include a final court of appeal for Commonwealth countries that have chosen to retain it.
The dam is being built on the Upper Macal River, one of the largest undisturbed areas of wilderness in central America, by Becol, a Belizean subsidiary of a Canadian multinational, Fortis Inc.
Bacongo says the environmental impact assessment of the dam, by the London firm Amec, was seriously flawed.
* the agreement between the Belizean government and Fortis could drive up electricity prices
*Amec wrongly identified rock at the site as granite, although it is softer
sandstone and shale fault lines near the site were removed from maps submitted to the government
*Amec's hydrological studies of the Macal were inadequate: at the height of the wet season the river's entire flow, Bacongo says, fitted in four small pipes.
The Upper Macal is home to rare and endangered species, including the tapir, Belize's national animal.
Some zoologists believe it has a high density of large cats, including jaguars, ocelots and pumas.
Unable to migrate
It is the only known Belizean breeding ground of a rare sub-species of scarlet macaw, with 1,000 survivors worldwide.
Sharon Matola, the founder of the Belize Zoo and a member of Bacongo, told BBC News Online: "If the dam is built it will flood the macaws' nesting area.
"That will eventually mean their extinction in Belize, because they don't build nests but live in holes in trees - and the trees they choose occur nowhere else.
"Tapirs need the special vegetation you find in the area ... and if the tapirs go, there'll be nothing to attract predators like jaguars.
"The dam won't give Belize energy security - it'll produce enough power to run three large hotels.
"We could burn sugar cane waste, which is abundant, or we could go on using the transmission line to Mexico, or join the new Central American grid that's being planned."
Images courtesy and copyright of Bacongo.