The amount of oxygen present removed by plants, animals, and organic material present in the water sample is the Biochemical
Oxygen Demand (BOD). It is calculated by subtracting
the DO level on the fifth day from the original level on the first day. Excessive
decomposing organic material and its accompanying colonies of aerobic bacteria
deplete the dissolved oxygen causing high BOD levels. The highest BOD
level was recorded at site 3 on April 8, 2004. On that day, an abundance of decomposing
plant material and human refuse was observed, explaining the high BOD
reading of 5.5.