My next question is, why tries the refraction, to refract something abouve the water? It should only refract things under the water. That is why it has the cut which I discribed on the top of the thread, because some things over the water are outside the viewport and can’t be refracted. I tried the same with the Source Engine and CryEngine… they are refracting it correctly, only things under the water.
Edit 1: Reflection is disabled 
