Ultrasonic Distance Sensor - HC-SR04

If waterproofed, in an iPhone waterproof “bag”, for waterparks and such, could an HC-SR04 sensor communicate underwater at 200cm, given that the programming specs are adjusted to the speed of sound in water.

Thank you, in advance!

If waterproofed, in an iPhone waterproof "bag", for waterparks and such, could an HC-SR04 sensor communicate underwater at 200cm, given that the programming specs are adjusted to the speed of sound in water.

No. You need submarine equipment and there it is called sonar.

No chance.
Look for sonar, or fish finders. Those have transducers that are suitable for underwater use.