Salt Water Monitoring

Hi all

Im interested in what would be involved in building a wireless salt water monitoring station, the station would be just over 4KM from the receiving station.
Im for now interested in monitoring Temp, Salinity, Water Level and water direction (graph tidal movement).

The station would be based near the north end of Blackman Bay Tasmania, Australia.
http://maps.google.com.au/?ie=UTF8&ll=-42.869296,147.860184&spn=0.097378,0.222988&t=h&z=13

Does anyone have any experience in this area, could you please explain what hardware/software/cost $ would be involved in a station like this

Thank You in advance

Greg