A tributary or affluent is a stream or river which flows into a main stem (or parent) river. A tributary does not flow directly into a sea, ocean, or lake. Tributaries and the mainstem river serve to drain the surrounding drainage basin of its surface water and groundwater by leading the water out into an ocean or some other large body of water.

A confluence is where two or more bodies of water meet together, usually referring to the joining of tributaries.

Reciprocal to a tributary is a distributary, a river that branches off of and flows away from the main stream.

The Anduin has many tributaries(about eight or nine known), being the river Entwash the greatest of them, and where the two rivers met, a mighty delta formed, measuring a hundred miles from the splitting of the Entwash to its final inflow into Anduin. This delta formed the Mouths of Entwash.

TerminologyEdit

'Right tributary' and 'left tributary' (or 'right-bank tributary' and 'left-bank tributary') are terms stating the position of the tributary relative to the flow of the mainstem river. These terms are defined from the perspective of looking downstream (in the direction the water current is going).