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.