public void setWaterTransparency(float waterTransparency) {
        this.waterTransparency = Math.max(0, waterTransparency);
        material.setFloat("waterTransparency", waterTransparency / 10);
    }
sets the water transparency default is 0.4f

@param waterTransparency the desired transparency (default=0.4)
jme3-effects/src/main/java/com/jme3/water/SimpleWaterProcessor.java