Nepal lake: Work begins to drain rising waters near Everest
Nepal's army has started work to drain rising waters in a lake near Everest at nearly 5,000m (16,400ft).
Scientists say that is vital to partially drain Lake Imja to stop it from bursting its banks with potentially devastating consequences.
Imja is one of thousands of lakes in the Himalayas formed by the melting of glaciers. But last year's earthquake may further have destabilised it.
It is the highest drainage project of its kind, the military says.
The altitude at which the work is being completed has posed logistical challenges for the army.
Rising temperatures are accelerating glacial meltdown and rapidly filling such lakes, threatening communities and infrastructure downstream.
With UN funding, Nepalese army personnel and villagers are working to reduce Lake Imja's level by three metres (9.8ft) in the next few months. Weather conditions are harsh, with workers facing the added risk of altitude sickness.
Lt Col Bharat Lal Shrestha of the Nepalese Army told the BBC that about 40 army staff were working alongside Sherpa and other highland community members.
The plan is to construct an outlet through a diversion channel and gradually release water over 45 days.
"We can work for only two to three hours in a day as most of the time it snows making it very cold in addition to the fog and wind," Col Shrestha said.
"Our personnel get headaches and altitude sickness from time to time and we make them descend to our lower camp where they can recover and eventually come back to work."
While troops were acclimatising, heavy equipment was airlifted to the site by helicopter.
Officials say the army was called in after two rounds of international bidding to complete the work failed to produce a contractor.
"This is the highest altitude disaster risk mitigation work ever performed by any army in the world," Col Shrestha said.
The draining of the lake is a part of a UN project to help Nepal deal with the impact of climate change.
Glacial lakes have broken their banks in Nepal more than 20 times in recent decades. Three of those incidents have been in and around the Everest region.
Nepal lowered the level of another dangerous glacial lake, the Tsho Rolpa, in the Rolwaling valley west of the Everest region, in 2000.
Many lakes in parts of the Himalayas are feared to have been weakened by a powerful earthquake which killed 18 climbers, as well as thousands of Nepalis, in 2015.