You'd need something super specialized, because water and rocks/earth block radio waves exquisitely well, and the churning water would be difficult to survive r

You'd need something super specialized, because water and rocks/earth block radio waves exquisitely well, and the churning water would be difficult to survive regardless. So perhaps some sort of camera + high sensitivity inertial measurement unit in an extremely rugged housing along with an ultrasonic data transmission system or something. All of which would be extremely custom and would likely require several iterations and vast expenditures of money and effort just to collect a little data.