The referenced script on this Behaviour is missing! Nothing happens(HELP!)

 #pragma strict
 
 var waterlevel : float;
 private var isUnderwater : boolean;
 private var normalColor : Color;
 private var underwaterColor : Color;
 function Start () 
 {
   normalColor = new Color(0.5f, 0.5f, 0.5f, 0.5f);
   underwaterColor = new Color(0.22f, 0.65f, 0.77f, 0.5f);
 }
 
 function Update () 
 {
   if ((transform.position.y < waterlevel) != isUnderwater)
   {
      isUnderwater = transform.position.y < waterlevel;
      if (isUnderwater) SetUnderwater ();
      if (!isUnderwater)  SetNormal ();
   }
 }
 
 function SetNormal ()
 {
   RenderSettings.fogColor = normalColor;
   RenderSettings.fogDensity =0.002f;
 }
 
 function SetUnderwater ()
 {
   RenderSettings.fogColor = underwaterColor;
   RenderSettings.fogDensity =0.03f;
 }