Terminology
'Right tributary' and 'left tributary' (or 'right-bank tributary' and 'left-bank tributary') are terms stating the orientation of the tributary relative to the flow of the main stem river. These terms are defined from the perspective of looking downstream (in the direction the water current of the main stem is going).
Where tributaries have the same name as the river into which they feed, they are called forks. These are typically designated by compass direction. For example, the American River receives flow from its north, middle, and south forks. Abbreviations "WFK" and "EFK" are sometimes used for "West Fork" and "East Fork".
Forks are sometimes designated as right or left. Here, the "handedness" is from the point of view of an observer facing upstream. For instance, Steer Creek has a left tributary which is called Right Fork Steer Creek.
Read more about this topic: Tributary