fiber optics cable connection

Would a radio link be more economic than fibre-optics?

Any bridges across this river?

Actually, there are so few options here that I'm truly surprised that you have to ask for advice. This must be your first job????

Micro wave link. http://www.dineshmicrowaves.com/training-kits.html

laser link. http://www.sigma-trainers.com/fiber%20optic.htm

put cable in galavanised tubes as weight and sink it along bottom.

place lead rings on cable and sink

You must have a big yard. Or you do it at night? Then you'll need a row boat - makes less noise.

Can use smoke signals. No bridge or ponding required.