In order to smooth out the waterfalls, I use a neutral density filter and a long exposure… 23 seconds in this case. The added benefit of doing that is that as people move in or out of the frame they generally don't show up in the final image, or if they do it's faint enough that they're super easy to Photoshop out. This little dude stood stock-still for the entire 23 second exposure and actually turned out to provide a really cool element to the final image.