Not necessarily. There's a lot of cr@p located in shipping channels and beneath bridges. You'd be amazed at the stuff people chose to dispose of in a body of water. Bridges are convenient for a quick dump, but a deepwater channel presents different challenges. Many heavy ships use depthfinders to make sure that they stay in the designated channel. You'd need to shutdown most commercial shipping to be able to do a dive operation because you can't have divers in the water with sonar banging away.
Also, depths of over 130 fsw require decompression for the divers. This may be the chief reason that the Navy is using marine mammals to identify sea mines -- it conserves your divers for mine clearing activities.