scripting question. turn component on/off

i want to turn a component on when i get below a certain y-coordinate, and then turn it back on when i go above said coordinate. i'm using this for an underwater effect. provided the code that im using so far. it is attached to my main camera, and the component i want to turn on/off is a projector that is also attached to my main camera. any help?

 using UnityEngine;
 using System.Collections;
 using UnityEngine;
 using System.Collections;
  
 public class Underwater : MonoBehaviour {
  
     
     public int underwaterLevel = 7;
      public Color newFogColor;
     
     
     public bool defaultFog = RenderSettings.fog;
     public Color defaultFogColor = RenderSettings.fogColor;
     public float defaultFogDensity = RenderSettings.fogDensity;
     
  
     void Start () {
         
         camera.backgroundColor = new Color(0, 0.4f, 0.7f, 1);
     }
  
     void Update () {
         if (transform.position.y < underwaterLevel)
         {
             RenderSettings.fog = true;
             RenderSettings.fogColor = (newFogColor);
             RenderSettings.fogDensity = 0.04f;
             
         }
         else
         {
             RenderSettings.fog = defaultFog;
             RenderSettings.fogColor = defaultFogColor;
             RenderSettings.fogDensity = defaultFogDensity;
             
         }
     }
 }