Looking to build out a mesh network with radios being mounted on customer's docks. This leaves 5-10' clearance above the water. Would 5ghz work better than 2.4ghz for this?

I'd go with 5.8.. shorter wavelengths, more bandwidth, less noise.. If it's in a marine type environment LOS doesn't sound like an issue.

Right, my main concern is the water. I'll use powerline bridges to get back into the houses.

Right, my main concern is the water.

You mean the reflection?

Correct. These radios will only clear the surface of the water by 5-10 feet.

Higher frequencies are more affected by water.

JP,

What am I looking at here?

These are signal graphs of radio links over water. Tide, and to a lesser extent thermal differences, have a HUGE effect on the signal if the link shoots over water, and either end is within 1/4 mile of the water.

Try using a 5.8 signal splitter, and 2 antennas.
You will have to play with the antenna seperation.
The idea being that the reflections will out of phase somewhat at each antenna, and will have a reduced effect on the performance of the link(s).

Has anyone tried circular polarization over water? If so, what frequencies did you use?