Black and white photography is a great medium for spotlighting textures, shapes and lines. Here, the patterns in the wake of the boat form a triangle which naturally points us to the subject. The ripples from the oars also draw us in their succession to the oars which draw us to the subject. And finally, the waves in the river itself point towards the rowers.
All of these lines and shapes tell us there is movement, which is important for an active image.
Interest, direction, and movement, this shot has all three. Add colour, and some of that would be lost.
In the image below, black and white photography works again. Here, flow is a significant and fluid movement in the lines of the curve of the subject's neck and shoulders and in the blurred background edges as well. The eye is directed to the dangling earring by way of lines and also light. Originally in colour, the teal tank top and yellow background took away from the flow and ultimately the subject.
Composing shots by seeing with your mind and eye in both colour and grayscale is helpful in discerning how best your image will present.