public void setRefractionStrength(float refractionStrength) {
        this.refractionStrength = refractionStrength;
        if (material != null) {
            material.setFloat("RefractionStrength", refractionStrength);
        }
    }
This value modifies current fresnel term. If you want to weaken
reflections use bigger value. If you want to emphasize them use
a value smaller than 0. Default is 0.

@param refractionStrength the desired strength (default=0)
jme3-effects/src/main/java/com/jme3/water/WaterFilter.java