Do you have a Thermocouple meter? If not get something like this;
Thermocouple sensorThen get Thermocouple wire (K Type) like this;
Thermocouple wireThen attach a connecter on one end, like this (male);
Thermocouple connectorThen twist the other end of the wires together, and add a drop of solder (the end that goes in the water).
Tie a sinker onto this end and lower into the murky depths, keep the plug end accessible (at dock), leave it there, and plug into meter whenever you want to see the data.
