Thanks guys. It´s really just a rather simple effect. The Wavefield water was way more complex (geometric waves, infinite water + LOD, shores, 'under-water-support'). The under water terrain shader is actually using the same fake caustics like implemented in Wavefield but it´s probably barely visible through the water refractions if you don't know. Also it's true that the diffractions aren't perfect at all, but I didn't spend any extra time in improving those when I re-implemented the water (it's not a new shader).

Just recognised that I forgot to mention (in the video description) that the shader uses cubic env-reflections for the skycube reflection which looks way better than the simple bumpmap-distorted reflections from the reflect-view-rendertarget. Thx.^^