China has blocked a tributary of the Brahmaputra as part of a major hydro-electric project, whose construction began in 2014.
The state-run Xinhua news agency is reporting that the blockage of a tributary of the Yarlung Zangbo river is part of China's “most expensive” hydro project.

About Brahmaputra river
The Brahmaputra in its upper reaches is called Yarlung Zangbo, after it originates from the Angsi glacier in western Tibet, southeast of Mount Kailash and Mansarovar Lake.

Indus treaty review coincidence
China’s move coincides with the debate in India on the careful assessment of Indus water flows into Pakistan following a cross-border raid in Uri that killed 18 Indian troops.
The project on the river Xiabuqu in Xigaze (Place), also called Shigatse, involves an investment of $740 million, the head of the project’s administrative bureau was quoted as saying.

Impact on India
Shigatse, a railhead of the Qinghai-Tibet railway, is a few hours driving distance away from the junction of Bhutan and Sikkim. It is also the city from where China intends to extend its railway towards Nepal.
It is as yet unclear whether the dam will have any impact on water flows towards India and Bangladesh — the two riparian states that are drained by the Brahmaputra.
So far, China has maintained that its dams do not restrict the flow of water towards India as they are based on run-of-the river principle.

Ambitious hydro power plans
China’s 13th five year plan has proposed significant hydropower expansion along rivers that also originate in the Tibetan plateau.

Although the plan does not mention any river specifically, it is anticipated that the new dams are envisaged along the Yarlung Zangbo, Lancang (Mekong) and Nu (Salween), all originating in the Tibetan plateau.

2013 MoU
India and China have set up an Expert Level Mechanism on trans-border rivers. In 2013, they signed a memorandum of understanding on trans-border rivers, under which China has been supplying data to India on water flows.