How are the headwaters of a river determined?

Question

I have been reading about the Mississippi river and all the folks that thought they had found the headwaters. I have been there and there are hundreds of lakes in that region, each fed with from streams. How do you determine which stream from which river is the source?

Answer 1

You don't or go crazy trying. In some rivers it is more or less obvious - the Nile goes south and virtually no other rivers join it. It rises when no rain has fallen in its valley because heavy rains fall on its lake origin.
Usually, rivers are tracked to their headwaters by looking at all the rivers that come in and choosing the longest one for bragging rights.
In the US, the longest river ends down at New Orleans after flowing by Saint Louis and Kansas City, Omaha and Bismark and if that doesn't sound like the Mississippi starting in Minnesota, it isn't. The Missouri River is much bigger at St.Louis than the Upper Mississippi, so by rights it should lead to the headwaters, but Ol'Miss was found by the French from the North and hit by the English from the East and nobody paid much attention to what was on the west side until it was too late. And besides Ol'Miss is straight - how could that right angle river be the main one?
The origin of Ol'Miss was moved several times because people found creeks flowing into lakes that were supposedly the headwaters, so they could go further upstream.