Oxygen found in water is referred to as dissolved oxygen and is measured in milligrams per litre. Aquatic organisms use this oxygen for survival. Measure dissolved oxygen using a dissolved oxygen meter, a device that can be used in the field at lakes, streams, ponds, rivers or oceans.
Calibrate the dissolved oxygen meter probes following the manufacturer's user manual.
Collect your water sample using a secure bottle. Make sure the bottle does not allow air to get in your sample. If you are collecting samples in the field, choose multiple locations with varying depths and distances. Dissolved oxygen results will vary depending upon those parameters.
Rinse the dissolved oxygen probes with distilled water to remove previous water sample leftovers.
Place the probe of the dissolved oxygen meter into the sample. Stir the probe. The dissolved oxygen reading will fluctuate. Wait for the dissolved oxygen meter reading to stop, or equilibrate.
Record results in your field or lab notebook and repeat steps for each water sample. In addition, record the date, time, location, depth and distance for each sample.
Clean the dissolved oxygen probes with distilled water and place the rubber coverings over the probes to avoid contamination or possibility of breaking.