Water conducts sound extremely well , better (and faster) than air.
I thinking in a very free form mode here but you could rip the
transducers off a couple of old fish finders and use em for tx and rcv.
units.
 I think these guys operate above 30 KHz.  You may be able to modulate
 enough info on to the carrier to do slow frame video.

----------
> From: Alessandro Zummo <azummo@ITA.FLASHNET.IT>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: OT: Radio Transmission in Water
> Date: Friday, March 06, 1998 12:50 PM
>
> Il 06-Mar-98, Jacques Audette scrisse:
>
> > I'm usually silent but since i already tought of the dtmf idea a while
> > ago for another project and noticed it could not work, i had to say it.
>
> > The only problem with dtmf is the speed. the detectors cannot lock fast
> > enough to get a normal bandwidth (usually a couple of ms). A solution
> > would be High Speed DTMF (I heard of it but never looked it up).
>
> I tought to use dtmf only for driving an r/c submarine,
> surely not for other purposes... i could enlarge the tone
> duration... anyway i should still evaluate the attenuation
> of a sound in the water... if someone knows about
> HSDTMF.. would be better :-)
>
>
> --
>
>    - *Alex* -
>
>   http://freepage.logicom.it/azummo/