Which statement is true about high BOD?

• A. It implies high dissolved oxygen
• B. It implies water has low organic waste
• C. It implies water has lots of organic waste and lower dissolved oxygen
• D. It implies water is free of bacteria

Answer: (C)

High BOD means there’s a lot of organic material in the water. Microorganisms, especially bacteria, work to decompose that material and in the process consume dissolved oxygen. As oxygen is used up, the water’s dissolved oxygen level drops, which can stress or kill aquatic life. So high BOD signals both abundant organic pollution and lower dissolved oxygen. The other ideas don’t fit: high BOD does not imply high dissolved oxygen; it indicates the opposite. It does not mean there’s little organic waste; it means there is a lot. It also doesn’t indicate the water is free of bacteria—BOD actually reflects microbial activity consuming the organic matter.