Instead of using lines to show the flow of the water, use fewer lines to outline any rough patches in the flow of water. For example, that rock would create some waves, maybe even some white water effects, so use lines to illustrate the flow of the water around that rock, and focus less on the water flowing down the smooth part of the stream. I hope this makes sense
Why so many lines? A lot less lines, make it to where the lines are only where the current changes, it looks like grass or something fell into the water the way you are doing it...