The above-mentioned article is an introduction to river-reading improving "your ability to read water, the language of rivers, and understanding all that the river is trying to communicate to you – its’ paddling audience".
The language of rivers is discussed using a vocabulary of "texture" and "colour".
As you moving water winding its’ way over rocks, ledges and around outcrops and around bends in the river bank, you’ll see a veritable kaleidoscope of changing colours and wave patterns. Each obstacle leaves a visual marker to its presence. By looking at the changing textures and colours you can decipher the river bottom, the level of difficulty of the water features, and ultimately, make a choice as to whether you ought to run, or not run, a rapid.
Reading whitewater is a lot like learning a language. The more you practice the better able you will be at quickly deciphering the message. Fluency comes once you can glance quickly at a set of rapids and “read” precisely where to paddle your canoe. Building upon the basic vocabulary of texture and colour will allow you to scout a safe route down your next rapid, or even more importantly, recognize when it would be safer to portage around it.