This is a paid asset, but now you can download Realistic Waterfall Prefab for FREE, but please remember this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Detail this asset from Unity Store: Original Link
Realistic Waterfall Prefab v1.5
>Compatible with Unity 2017
Realistic waterfalls are hard to realize. This time, we give you complete waterfall prefabs. You can use them directly in your game! There are three styles of waterfall: particle style, refraction style and standard mesh style. And standard mesh style has three levels of quality. According to your efficiency concerns, you can use the proper one of them~
>>20+ textures you can acquire
>>4 SoundFX(wav) you can acquire
>>5 Waterfall Prefab you can acquire
>>Compatible with SRP ,URP , HDRP