Photographing water flow, such as a river or waterfall can lead to some impressive images. If you would like to create a smooth effect to the water, set the camera mode to shutter priority and slow the shutter speed. This of course allows more light into the image so you may need to decrease the exposure using the exposure compensation setting on your camera. You should also consider whether you need to use a tripod for stability.
The following picture, which I took a couple of years ago, used a shutter speed of 1/8 of a second. I braced the camera (and myself) on a rocky shelf to reduce the chance of camera shake. I lost elements of the colour through having a longer exposure so I've brought out some of the colours in Photoshop on this occasion.
If I had the opportunity to revisit the scene and take a similar picture, I would use a polarising filter to help bring out the different colours and I would experiment with longer exposures, compensated for by adjusting the exposure compensation setting in the camera functions. You can read an introduction to polarising filters in my post here.
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