High Quality Content by WIKIPEDIA articles! The R tei River is a tributary of the Cascue River in Romania. 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 act of tributaries. Reciprocal to a tributary is a distributary, a river that branches off of and flows away from the main stream. Distributaries are most often found in river deltas.