Latourell Falls, Columbia River Gorge, Oregon
Fujifilm X-E2, 18-55mm
Most of my photography is of waterfalls, cascades, lakes and streams. There are certain "tricks of the trade" photographers use to create attractive images involving water. With some exceptions, we want the water to appear as the great landscape photographer Willard Clay described as "flowy." You can see the impact of that in the above shot from the Columbia River Gorge. A slow shutter speed created a "flowy" look in the water.
Many folks photograph waterfalls in bright sunlight -- usually a big "no no" -- because they are there at the wrong time. Bright light means faster shutter speeds and generally harsh, unpleasing images. An overcast day is ideal but, barring that, then consider getting to the waterfall area at or just after sunrise and within an hour of sunset. Your camera will need to be on a tripod and you should use a remote shutter release to eliminate blur from vibration. A waterfall image often means seeking the best of both worlds -- maximum sharpness for what needs to be sharp and the right amount of "flowy" water.
This isn't to say that we always want "flowy" water in an image. Freezing the action with a high shutter speed can work in the right situation, such as in this wildlife "chase" scene:
Virgin River, Zion National Park, Utah
Canon EOS 20D, 500mm f.4L, 1/160 sec. @ f/4
1/160 second was enough to stop some of the action. I didn't want all of it completely frozen as it might dilute the impact of the scene.
Experiment with different shutter speeds to see what works best for you.