Rivers are a basic feature of nearly all maps. Road maps usually show them as light blue so they will not conflict with the roads that run alongside them, and to avoid a second set of strong line elements that would confuse the eye. Raven lowers roads in the design hierarchy and clearly shows the interesting and often beautiful pattern of rivers (above).
But, emphasizing rivers reveals some confusing paradoxes. Important rivers demand heavier/darker lines than unimportant ones, of course, but what determines importance? The volume of water? In that case, the Colorado River should be shown by a line getting steadily wider as far south as Lake Powell, but then steadily narrower until it vanishes before reaching the Gulf of Mexico. Logical, but it would look nonsensical (below).
Or, importance could be measured by the length of the stream. In that case, the Missouri should be shown by a much wider line than the Mississippi at their confluence at St. Louis, but the Mississippi is by far the larger stream, so THAT would look nonsensical.
Finally, what do we do about name changes over the length of the stream? Many cultures give each major portion of a river its own name. The Spanish did that a lot, but it happened in the British colonies, too (the Yadkin in North Carolina becomes the Pee Dee in South Carolina, as below).
In Wyoming, the Wind River becomes the Bighorn River after flowing between Owl Creek and Bridger Mountains. Nearly all streams are ultimately fed by smaller and smaller upstream tributaries, and it's mostly historical accident that determines how far upstream the name officially applies.
So ... if you are puzzled by a Raven map showing a dry wash as a river, or a named stream rising much further up its basin than some other source does, we probably did that for a reason.