private void OnTriggerEnter2D(Collider2D collider)
    {
        Collectible collectible = collider.GetComponent <Collectible>();

        if (collectible && collectible.CanCollect())
        {
            waterSprite.AddToTargetList(collider.gameObject);
        }

        // If we just landed in some water, then tell the WaterSprite to refill if it isn't already full
        if ((1 << collider.gameObject.layer) == AI.WaterLayermask && !inventory.WaterLevelFull())
        {
            waterSprite.AddImmediateToTargetList(collider.gameObject);
        }
    }