A river and its tributaries are?

Answer 1

the main river and all of its tributaries are called a river system. The land drained by the river system is called a drainage basin. Drainage basins are separated by the high land in between, known as a divide or watershed.

Answer 2

A river and its tributaries are part of a larger water system called a watershed. The watershed is a ridge of land that separates waters flowing to different rivers, basins, or seas.