Is high BOD good or bad?

If Biochemical Oxygen Demand is high then it will have negative effects on aquatic ecosystems as fish and other aquatic life may suffocate in oxygen-depleted waters.

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
• Human-Wildlife Conflict
• UPSC Environment and Ecology