need help with javascript for underwater blur effect

I have an underwater script that produces a fog effect and I am trying to make a blur effect as well, but when I tried adding the blur, I get the error:

NullReferenceException: Object reference not set to an instance of an object

Here is the script I am using:

 var underwaterLevel = 19;
 
 private var defaultFog;
 
 private var defaultFogColor;
 
 private var defaultFogDensity;
 
 private var defaultSkybox;
 
 var noSkybox : Material;
 
 
 
 function Start () {
 
     defaultFog = RenderSettings.fog;
     
     defaultFogColor = RenderSettings.fogColor;
 
     defaultFogDensity = RenderSettings.fogDensity;
 
     defaultSkybox = RenderSettings.skybox;
 
     camera.backgroundColor = Color (0, 0.4, 0.7, 1);
     
 }
 
 function Update () {
     if (transform.position.y < underwaterLevel) {
         RenderSettings.fog = true;
         RenderSettings.fogColor = Color (.5, .6, .6, .6);
         RenderSettings.fogDensity = 0.08;
         RenderSettings.skybox = noSkybox;
         GetComponent("BlurEffect").enabled = true;
     }
 
     else {
         RenderSettings.fog = defaultFog;
         RenderSettings.fogColor = defaultFogColor;
         RenderSettings.fogDensity = defaultFogDensity;
         RenderSettings.skybox = defaultSkybox;
         GetComponent("BlurEffect").enabled = false;
     }
 }

Anyone know what I need to change to fix this? I'm using version 3.5

The part that is giving errors is this:

GetComponent("BlurEffect").enabled = true;