By Jill McGivering
BBC News, Kazakhstan
In summer sunshine, the waters of Lake Balkhash shimmer a startling bright blue.
Lake Balkhash plays a key role in eastern Kazakhstan
At weekends, the beach is busy with local families, splashing in the waves and sunbathing on the sand.
Behind them loom the towers of the copper smelting plant at the heart of the Balkhash town.
The lake, the fourth largest in Central Asia, situated about seven hours north-west of Kazakhstan's main city, Almaty, is the lifeblood of this arid region.
It supports industry, agriculture and a population of three million people. But scientists now warn the existence of the lake is under threat.
A local couple, walking home from the lakeside with their young daughter, said the level of the lake had fallen dramatically in the last few decades.
Egor pointed to a tall metal water tower now about 15m (49 feet) from the shoreline. Back in the late 1960s, he said, he remembered it being so deeply submerged, they used to climb up the tower and dive into the water.
"And see these cafes on the shore?" he added, pointing to the back of the beach. "This was all water before."
Some of this drop in water level may be natural. Some scientists point out that the lake does have a natural cycle which accounts for much of that rise and fall.
Mikhael Sirotkin measures the water twice a day
But it is also clear that the biggest threats are man-made. The lake's main source is the River Ili, already depleted by a reservoir created upstream and heavy agricultural use. The River Ili also flows through China and the main concern now is plans by the Chinese authorities to divert most of the river water to support the rapid development of western China.
"The population of China is growing which isn't good for the ecology because they will use more water," said Mels Eleusizov, a prominent campaigner with the ecological group Tabigat.
"That's why the danger is absolutely real. We can solve the local problems ourselves, but we have to explain to China that if Balkhash dies, it will affect them as well."
Mikhael Sirotkin, a retired local scientist who has spent more than 30 years studying the lake, is also anxious. He wades out to a concrete measuring platform in the lake twice a day, morning and evening, to measure the water level and record his findings.
He has written to the government to express his concern about the need to protect the lake, but says the reply he received just told him not to worry.
"Most people are so ill-informed about this problem," he said. "And they'll get a big shock - not today, but in the future - when the water level goes down.
"Then everybody will ask why and how this happened because now people don't know what's going on. How can they be worried if they don't understand the problem?"
Many local people do seem complacent. I came across a small group of middle-aged men, sitting in the shade of reeds by the lakeside in their swimming trunks, enjoying lunch after a morning's social fishing.
They scoffed when I asked them about danger to the lake. Yes, the water level was much higher in the 60s, they said, but now it is rising again. It is nothing to worry about, they said.
But Natalia Vorobeova, a biological scientist and government adviser, said the future of Lake Balkhash could bring an even greater environmental crisis than the drying up of the Aral Sea - now acknowledged as one of the world's worst ecological disasters.
If China did divert the waters of the River Ili, she said, the whole climate in the Balkhash region would be affected.
The lake has been affected by heavy agricultural use
"There'll be more desert," she said. "It will be just the same as around Aral. And Aral was less populated than here. This is a very populated area. Emigration will start, people will move. It will be a catastrophe."
And according to Mels Eleusizov, if steps are not taken to protect the lake's future, the consequences would be felt far beyond not only the Balkhash region but also Kazakhstan itself.
"It isn't just our national treasure," he said. "It's a treasure of the whole world. We all know how many global problems Aral created, not just regional ones - it affected China, Mongolia and even Europe. To let the same thing happen in Balkhash would be a crime."
Today this vast lake is a great natural beauty as well as a great natural resource. But according to scientists here, unless action is taken quickly, all of this, from the waters, fish, bird life and local communities, could disappear in as little as a decade, presenting the world with a fresh ecological disaster.