public void setUseCaustics(boolean useCaustics) {
        this.useCaustics = useCaustics;
        if (material != null) {
            material.setBoolean("UseCaustics", useCaustics);
        }
    }
set to true if you want caustics to be rendered on the ground underwater, false otherwise

@param useCaustics true to enable rendering fo caustics, false to disable
it (default=true)
jme3-effects/src/main/java/com/jme3/water/WaterFilter.java