Mels Eleusizov heads the Kazakh nongovernmental organization Tabigat (Nature). He said the Irtysh and Ili rivers, which both originate in mountainous areas of Xinjiang before crossing into Kazakhstan, are being increasingly drained to serve China's needs.
"For Kazakhstan, the most alarm concerns two rivers -- the Ili and Irtysh," Eleusizov said. "The new infrastructure and factories in Xinjiang consume a lot of water. The drinking water needs are increasing, too. If China continues to increase water consumption in the area, it will certainly affect the water resources on our side."
The Ili flows through Xinjiang into southeastern Kazakhstan and terminates in Lake Balkhash.
The Irtysh rises in China's Altai Mountains and also crosses into northeastern Kazakhstan, before flowing through Lake Zaysan to the Russian city of Omsk and then into the Ob River.
The increasing usage of river water in Xinjiang, which has relatively few water resources of its own, is inherent in Beijing's aim of attracting ethnic Han Chinese to the region and developing the local economy.
Ann McMillan, a scholar at Griffith University in Queensland, Australia, has been researching the interdependency between Xinjiang and Central Asia.
"There's actually a lot of concern coming out in China in the government [media]," McMillan says. "There have been reports about the water table dropping, especially around Urumqi, the capital of Xinjiang. So they are aware that they've got major problems. And they've even started charging for water in some places. But for their development to go ahead, they need water. So you've got a 'Catch 22' situation."
The Irtysh and Ili are crucial sources of fresh water for the Kazakh population. Both also play a vital role in the economy, providing water for the industrial, agricultural. and fishing sectors.
Myrzageldy Kemel is a member of the Kazakh parliament's Committee on the Protection of the Environment and Ecology. He talked about the environmental consequences of the increasing usage of the Ili's water:
"If the level of the [Ili] River decreases, the environment along the banks will be affected drastically," Kemel said. "Local citizens will suffer a lot. Now, nobody is paying attention to this, although in about 50 years [the situation] might be even worse than in the Aral Sea."
The Aral Sea has lost three-quarters of its volume since 1960, when Soviet-era planners began diverting its feeder rivers to irrigate cotton fields. The Aral Sea is widely acknowledged to be one of the world's worst man-made environmental disasters.
The United Nations Development Program (UNDP) has warned that Kazakhstan's largest lake, Lake Balkhash, is in danger of drying out if Astana does not adopt better water management practices or else gain Chinese cooperation over the usage of the Ili, the lake's main contributor.
The current construction by China of a canal -- 300 kilometers long and 22 meters wide -- to reroute water from the Irtysh is also of great concern.
Abai Tursunov is a professor at the Kazakh Institute of Geology and Geography in Almaty. He said he is worried about the environmental impact when the canal becomes fully operational, which is estimated to be in 2020.
"The completion of the canal will affect us drastically," Tursunov said. "Power stations will be very much affected. Nobody is raising the issue, but gradually all of this can lead to major environmental problems."
Hydropower stations and factories are located along the Irtysh, while the Irtysh-Karaganda canal makes agriculture possible in central Kazakhstan. The river also provides drinking water to the capital, Astana, as well as to three other major cities -- Karaganda, Semipalatinsk and Pavlodar.
Chinese authorities have provided little information on the canal project. But speaking to RFE/RL's Kazakh Service, China's ambassador to Kazakhstan, Zhou Xiao Pei, tried to be reassuring: "We currently use 10 to 20 percent of the [Irtysh's] waters. We are building a new infrastructure. [But] we are going to use no more than 40 percent [of the water]."
In 2001, Kazakhstan and China signed an agreement aimed at facilitating cooperation on trans-boundary water management. Through consultations, the two states agreed to share information concerning the Irtysh.
Zhakybay Dostay, also of the Kazakh Institute of Geology and Geography in Almaty, said the talks have led nowhere so far.
"The [joint Kazakh-Chinese intergovernmental] commission meets every year without results," Dostay said. "They just give figures, make statements and sign documents. The problems remain."
Kazakh President Nursultan Nazarbaev visited Xinjiang in September. But there is no indication that he raised the issue of trans-boundary rivers with Chinese officials.
(Merhat Sharipzhanov, director of RFE/RL's Kazakh Service, contributed to this report.)