RE: DEEP WATER: Transmission?
That's a very interesting project.
I would start by taking photographs ! It's easy to implement a mechanical mechanism to take the photograph. It could be based on a timer.
However, you do not know how your camera will land ! So installing 6 cameras viewing in each direction and triggered at the same time.
The main pb is : how to handle pressure ? How much pressure ? about 80 bars [X(] [X(] [X(] ....
I fear the bottom part of the lake is VERY dirty [:'(] ...