This is the 4290th most frequent Portuguese word.
afluente
A tributary (a stream or river that flows into a larger one).
In this sentence, 'afluente' is used to describe a smaller river or stream that flows into a larger one.
O rio principal conta com vários afluentes menores.
The main river has several smaller tributaries.
Here, 'afluentes' refers to the various streams and rivers contributing water to larger rivers in a geographical area.
Aquela região é particularmente rica em afluentes de rios grandes.
That region is particularly rich in tributaries of large rivers.
In this context, 'afluentes' is used in a more technical sense to refer to the waterways studied in the field of hydrology.