Wave pressure sensor


One thing I've been curious about is using OpenROVs to do stationary fish counts for a time, but move them from place to place, taking note of the wave environment around them. I.e. Do places with bigger waves have different fish communities. I've been looking around for wave height sensors, but they're all rather large and 3K each (at bare minimum). Has anyone figured out a way to build a cheap wave or water pressure sensor to get at wave heights? I'd imagine that depth sensors could somehow be adapted...and not break the bank.