the Mississippi headwaters is a kind of thing that is located in the Mississippi river.
The Headwaters of a river are it's origins. The multiplicity of small streams that converge to form the main body of the river proper.
Itasca.
Lumber river
CANADA
The source of river is known as its headwaters. In the example of the Mississippi River, its headwaters is Lake Itasca in Minnesota.
Mississippi
The "source", or its "headwaters"
headwaters
The Meander comes after the River Source
It is the source, or the headwaters.
Pennsylvania
Headwaters of the Amazon River
Mississippi
The start of a river is its headwaters and, just in case you were wondering, the end is its mouth.