What happens if BOD is low?

If Biochemical Oxygen Demand is Low, it is a general indication that the water is pure as less oxygen is being depleted.

High Biochemical Oxygen Demand is caused by organic pollution. The higher the organic pollution, the higher the biological oxygen demand. 

For more relevant articles refer to the links given below:

• UPSC Environment and Ecology Questions
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• UPSC Environment and Ecology