The river does not have a mind, so any decisions on what actions to take in the name of the river are actually conducted by a person/organisation. In that case it is the person/organisation that becomes responsible. So the river is just a pointer deference to another entity. Just like a corporation is a pointer deference to the shareholders.
It could also be akin to the guardian of a minor, whilst a minor may have a mind, they wouldn't necessarily be in charge of making decisions regarding legal recourse, or in some cases personal health. If we pursue this train of thought, there could be some expectations for the "legal guardians of rivers" to justify what course of action they should take on behalf of such a thing, in that they may be expected to ensure the health and longevity of the river, and hopefully improve the quality of life for all living things in and around rivers.
As I said the point of the river, is longevity and therefore just as a corporation optimizes for corporate profit a corporation representing the river optimizes for the river's longevity. I don't see how much difference there is between any corporation representing the profit motive of shareholders vs. a corporation representing the environmental motive of a natural resource. They are both simply ideas personified.
Currently people simply plunder natural resources where their longevity is an after thought and not really incorporated into the profiteering of their consumption. This has to change.
Why is the point of a river longevity? Left to their own devices, rivers change course and dry up. The key characteristic of a river is a flow of water not longevity
