I can't resist this thread. First the facts. Indus River originates in China and then flows through that country into disputed J&K, but even if we overlook that it's journey through 'India' is short before it entires Pakistan. Possibly upward of 94% of Indus flows through Pakistan with rest of the 6% shared by China and India. So clearly by that measure it is a Pakistani river. If source is used as criterion then it is a Chinese river.
But beyond that is the issue of impress or impact. Indus has nominal effect on China or India as it is literrally on their extremities barely touching the countries major populations which are far away. However Indus as it flows through it's 94% journey through Pakistan impacts almost every region of the country and directly nourishes water to all of Pakistan. Indus is like the human artery Aorta that feeds the entire body. Almost every farming field in Pakistan that is green is being fed by the mighty Indus river system. Indeed the Indus is more significant to Pakistan then Nile is in Egypt as that rivers runs through at least 5 African countries before entering Egypt.
In fact there could be no Pakistan WITHOUT Indus. Our history, our economy, our entire existence is premised on the River Indus. Anybody who has doubts about that can test that contention. Draw a computation that severs the Indus River flow to zero and see the effects. By the week Pakistan would begin to turn into desert and farms would dry up and country would face mass starvation and civil disorder as water would run out across huge swathes of the country.
It is histories ironies that the land that gave birth to the name India [specifivally Sindh province] today is not known by that name but countries or lands far and wide that have NOTHING to do with the historical cradle that birthed this name carry it, examples are Indonesia, India, Indiana, Indies [West], Indochina etc.
But Pakistan being divorced from it's historical legacy is not unique. Today we have a country called Romania that has zilch to do withthe Roman Empire and on the contrary that land that birthed that great empire is called Italy.
Other examples are Asia. Originally this meant the Anatolian [Turkish] coast as opposed to Europa [Greece]. Then it became attached to all of modern Turkey [Asia Minor], then moved to being mean the entire continent of Asia. Today in USA Asia often means Japanese, Chinese etc, in UK it means Paks, Indians etc and calling Turks Asian is almost unknown.
With referance to India, River Ganga occupies a gravitas in that country that is analgous to Indus in Pakistan, Nile in Egypt etc. If you look at the number of Indians who live on or in the watershed of Ganga [over 60% or 700 million Indians], major population centres, pivotal states like Utter Pradesh, New Delhi the capital, Hindu holy sites like Varanasi leaves no doubt that Ganga definese India and Indian history.
The story of Indus is story of Pakistan, the story of India is story of Ganga. Indeed India is
Gangadesh.
At a personal level, ever since I read Aitzaz Ahsan's Indus Saga ~Making of Pakistan which had a profound influence on my thinking, I take pride that Indus River has been one of the four cradles of human civilizations and that Pakistan needs to celebrate and own like Egypt, Iraq, China do.