Your issue is related to the dynamic range of your camera. The sensor of a camera cannot capture such as wide variety of tones as your eyes, the range between absolutely white and absolutely black is much more reduced than the one you can see when you look at the waterfall scene.

There is not much you can do about this, as it depends on your camera and in no case it will be able to capture all the range you see.

You have a couple of options though. First, make sure you shoot in RAW, as JPG compression reduces the dynamic range, and try to post-process the sky and the rest separately, low the exposure of the sky using some kind of mask in the editing software you are using and brighten the rest.

Other thing you can do is called bracketing: taking several shots of the same scene (you will need a tripod for that) with different exposure and them combine them, use the lower exposed ones for the sky area and the higher exposure ones for the rest. You can look for that option in your camera instruction manual.