How to Photograph Waterfalls: Getting Silky Smooth Water with the Right Settings
To get silky smooth water in waterfall photos, use a shutter speed of 1/4s to 2 seconds, ISO 100, and aperture f/8-f/16 on a tripod. In daylight you will usually need a neutral density filter. The longer the shutter speed, the smoother and silkier the water appears.