Try to Google In Situ Sondes.  I had one that recorded salinity, conductivity, depth, temperature.  It looks like a metal probe and you can attach a cable if you want to move to different depths, locations.  The depth feature had to be adjusted to baromtric pressure.  There may be other companies that sell these.  The one I had found the approximate intensity and frequency of salt influence into a coastal wilderness.  

Thera miniature sensors produced by Star-oddi. Please look at http://www.star-oddi.com. I used temp sensors and they are quite reliable.

Thanks for your input ^^. 

I will check them