Thermometers are used to measure the change in water temperature between two points- the test site and a site one mile upstream. It is important to match as closely as possible the physical conditions at these sites- current speed, amount of sunlight reaching the water, and the depth of the stream. To reduce errors, the same thermometer should be used at both sites.

Check the thermometer before using. Make sure the glass is not cracked and the red fluid is together and not separated. Hold the thermometer towards the top so that the warmth from your hand does not affect the reading. Begin by taking the air temperature in degrees Celsius. Record the air temperature in the appropriate place on the forms.

Temperature testing Procedure:

1. At the site where the other water quality tests are being performed, lower the thermometer four inches below the water surface.

2. Keep the thermometer in the water until a constant reading is attained (approximately two minutes).

3. Record your measurement in Celsius.
   (To convert from Fahrenheit to Celsius, subtract 32 and multiply by 5/9.)

4. Repeat the test approximately one mile upstream as soon as possible.

5. Subtract the upstream temperature from the temperature downstream using the following equation:
   temp. downstream - temp. upstream = temp. change

6. Record the change in temperature.