China-India fear 'water war' over two mega-dams on the same river : 

India is concerned that a proposed Chinese mega-dam in Tibet would cut a major river's flow by as much as 85% during the dry season. New Delhi is acting swiftly to carry out its own plans for dam development after realizing this. Four people with knowledge of the situation and a government study that Reuters examined provided this information.

The Indian government has been investigating a number of projects to regulate the water flow from Tibet's Angsi Glacier since the early 2000s. Downstream, this canal affects or controls the lives of about 100 million people in Bangladesh, India, and China. However, fierce and violent opposition from the people of the nearby state of Arunachal Pradesh has thwarted India's aspirations. Residents worry that building a dam will drown their communities and ruin their way of life.

In the meantime, China said in December of last year that it will construct the biggest hydroelectric dam in the world on the Yarlung Zangbo River in a border region right before the river enters India. This raised fears in New Delhi that the river may be used as a weapon by its longstanding geopolitical foe, which also has territorial claims in Arunachal Pradesh.
The Siang and Brahmaputra are the names of the rivers that flow into India from Tibet's Angsi Glacier.

Senior Indian officials, speaking to Reuters on condition of anonymity due to the sensitivity of the matter, said that meetings have been ongoing this year to accelerate construction. In July, Prime Minister Narendra Modi's office also held a meeting on the subject. In May of last year, India's largest hydropower company, protected by armed police, gathered survey equipment at the potential site of the "Upper Siang Project" dam on this river. Once the survey is finished, it will become India's largest dam.  Delhi's worries about the effects of China's dam have been mirrored in an evaluation by the Indian government. Although Beijing has not made public the dam's specific plans, the analysis, which was reviewed by Reuters, is based on earlier research conducted by organizations with ties to India. The evaluation also included the anticipated scope and magnitude of the Chinese project, which is predicted to cost around $170 billion. 

Delhi thinks that 40 billion cubic meters of water might be controlled by the Chinese project, based on papers and sources. During the non-monsoon months, the effects would be most noticeable in the border areas of India. However, this would be somewhat mitigated by India's own "Upper Siang Project," which has a 14 bcm capacity. Once constructed, it would thwart Beijing's attempts to control river flows while also enabling India to discharge water during the dry season.

A representative for China's Foreign Ministry responded to inquiries from Reuters on the subject by stating that the project is being implemented with rigorous scientific study centered on environmental and safety protection. The speaker went on to say that downstream nations' geology, environment, and water resources will not be adversely impacted.

The spokesman said that China has always maintained long-term contact and collaboration with downstream nations like Bangladesh and India, as well as a responsible stance toward the development and usage of transboundary rivers.