Both water and air temperature should be recorded while collecting the sample.
A well protected red spirit glass thermometer is robust and safe to use.
Mercury thermometers are not recommended due to the environmental hazard if broken.
An alternative is an electronic thermometer. Beware of the illusion of accuracy simply because they may read to a fraction of a degree. Immersion, especially in salty water, is generally fatal for electronic devices.
When buying the thermometer it is suggested you look at several and choose one which reads about the middle of the range of temperature at the time.
If the range of the thermometer is appropriate it can be checked in melting ice and boiling water to establish whether or not any correction is required.
For example, my thermometer is fairly well calibrated by 'rounding down' to the nearest lower whole degree.