What's causing my NPC Controller to invert? Please Help!!

I'm trying to make a NPC Controller race along a track using waypoints to guide it. I've checked to make sure that the waypoints themselves have the same y value, are in order in the inspector, and are all at the same rotation. But, as soon as I play my game, the NPC Controller immediately rotates vertically, and transforms it's y value so that it's positioned nose down and vertical above the water. I don't know what's causing this, but I wanted to see if it's maybe something in the code. If anyone would be willing to either provide new code/inform me of what to edit, it would be greatly appreciated. Here's the code for reference. Thank you so much!!

 var currentWP: int = 0;
 
 //the array of waypoints in order of visiting
 //can be made up of any game objects
 var waypoints: GameObject[];
 
 var speed: int = 5;
 var rotationSpeed: int = 2;
 
 //how close to get to the waypoint to consider having reached it
 var accuracy: Number = 5;
 
 function Update () 
 {
     if(waypoints.length == 0) return;
     if(Vector3.Distance(waypoints[currentWP].transform.position,transform.position) < accuracy)
     {
         currentWP++;
         if(currentWP >= waypoints.length)
         {
             currentWP = 0;
         }    
     }
     
     //rotate towards target
     var direction = waypoints[currentWP].transform.position - transform.position;
     transform.rotation = Quaternion.Slerp(transform.rotation,Quaternion.LookRotation(direction), rotationSpeed * Time.deltaTime);
     transform.Translate(0, 0, Time.deltaTime * speed);
 }