The Smart Rock is a submersible sensor suite that monitors water depth, temperature, turbidity, and salinity (EC) of a small stream over time and designed to be built by anyone with or without extensive experience in electronics. The device currently costs ~ $200 with these specifications and custom parts and takes about 10 hours to assemble and program.
For more information please visit the following link:
https://github.com/OPEnSLab-OSU/SmartRock/wiki