You seem to be assuming that it's entirely flooded. Seems probable that there are areas that are partially flooded, entirely flooded, or flooded and filled with

You seem to be assuming that it's entirely flooded. Seems probable that there are areas that are partially flooded, entirely flooded, or flooded and filled with wreckage. ie, an open water ROV may not be at all appropriate. Certainly if the answer was actually as simple as "buy this off the shelf thing" then all the smart people over there would've figured that out at some point in the last 3 years.