OnTriggerEnter Not working

Hey guys this problem is aboute the function OnTriggerEnter it doesnt work and when i pud it in the Update it works only i need it to work when my player is in the water Collider What did i do wrong??? thanks

var WaterLevel : float;
var useGravity: boolean;
var Player : GameObject;
var useBlur : boolean;
var Bubbels : GameObject;

private var defaultFog = RenderSettings.fog;
private var isUnderwater : boolean;
private var normalColor : Color;
private var underwaterColor : Color;
private var defaultSkybox = RenderSettings.skybox;
var noSkybox : Material;

function Start () {
    normalColor = new Color (0.5f, 0.5f, 0.5f, 0.5f);
    //0.22f, 0.80f, 0.80f, 0.5f)
    underwaterColor = new Color (0.80f, 0.85f, 0.75f, 0.5f);
    RenderSettings.fog = true;
    Bubbels.active = false;
    camera.GetComponent(Blur).enabled = false;
    camera.GetComponent(Fisheye).enabled = false;
}

function OnTriggerEnter (Player : Collider){
    if ((transform.position .y < WaterLevel) != isUnderwater) 
    {
         isUnderwater = transform.position.y < WaterLevel;
         if (isUnderwater) SetUnderwater ();
         if (!isUnderwater) SetNormal ();
    }
} 
//function Update () {
//   if ((transform.position .y < WaterLevel) != isUnderwater) 
//    {
//         isUnderwater = transform.position.y < WaterLevel;
//         if (isUnderwater) SetUnderwater ();
//         if (!isUnderwater) SetNormal ();
//    }
//}

function SetUnderwater() 
{
   //The Bubbels are a particle renderer Attached to The Player
   Bubbels.active = true;
   RenderSettings.fog = true;
   RenderSettings.fogColor = underwaterColor;
   RenderSettings.fogDensity = 0.10f;
   RenderSettings.skybox = noSkybox;
   camera.GetComponent(Blur).enabled = true;
   camera.GetComponent(Fisheye).enabled = true;

 }

function SetNormal() 
{
   Bubbels.active = false;
   RenderSettings.fog = defaultFog;
   RenderSettings.fogColor = normalColor;
   RenderSettings.fogDensity = 0.03f;
   camera.GetComponent(Blur).enabled = false;
   camera.GetComponent(Fisheye).enabled = false;
}
	// Turn this collider into a trigger on startup
	collider.isTrigger = true;

first. do you have your collider triggered? second where did you put this script?
and you’re just checking when a trigger is entered, you should check it when the trigger exits too.

Check here, 2nd reply

Maybe it can help you