Biochemical Oxygen Demand (BOD) is a measure of the quantity of dissovled oxygen used by bacteria as they break down organic wastes. BOD directly affects the amount of dissolved oxygen in rivers and streams. The more rapidly oxygen is depleted in the stream, the greater the BOD. This means less oxygen is available.

1. Submerge the small tube (0125) into the water sample.
2. Carefully remove the tube, keeping the tube full to the top.
3. Cap the tube.
4. Wrap the tube in aluminum foil and store it in a dark place for 5 days.
5. Unwrap the tube. Add two Dissolved Oxygen TesTabs (3976) to the test tube.
6. Cap the tube. Make sure there are no air bubbles. Invert until tablets have disintegrated. Wait 5 minutes.
7. Compare the color of the sample to the Dissolved Oxygen color chart.

The difference in the Dissolved Oxygen level between the uncovered tube and the covered tube is the Biochemical Oxygen Demand (BOD) of the water sample.

The detriment of high BOD is the same as low dissolved oxygen: aquatic organisms become stressed, suffocate, and die.