This is the first time I've had a go at taking long exposure photos of waterfalls but the Huawei P20 Pro made it easier to do and no need for an ND filter over the lens which is what all the other photographers at Lumsdale near Matlock in Derbyshire where doing with there DSLR cameras.
I setup on the rock with my P20 Pro and a small JOBY GripTight ONE Micro Stand to keep the phone steady.
I then went in to the P20's camera app settings and set the timer to 2 seconds to further reduce camera shake when tapping on the shutter to get sharper photos. Then switched to the Light Painting mode and selected the Silky Water mode and press the shutter and the Huawei phone does the rest for you.
I later edited the my favourite photos from the day in the Google Photos app to tweak the light and colour a bit.