Brahmaputra https://en.wikipedia.org/wiki/Brahmaputra_River is another notable river whose upper course was not well known till fairly recently.

What fills me with wonder and awe is that it is believed to be older than the Himalayas. Yet it cuts through the Himalayas, originating further North but traveling South, to eventually drain into the Bay of Bengal, sharing the delta with Ganges -- I would be hard pressed to find a more apt metaphor about overcoming Himalayan obstacles.

The river Indus shares the source, Manasarovar with Brahmaputra. Indus lines the subcontinent on the West, draining into the Arabian sea, while Brahmaputra lines it on the East. So essentially, one can consider the subcontinent to be encircled by water.