Which category represents grossly contaminated water?

• A. CAT 2: Heavily contaminated
• B. CAT 4: Baseline
• C. CAT 1: Grossly contaminated
• D. CAT 3: Moderately contaminated

Answer: (C)

Contamination levels are used to decide what safety measures and procedures are needed in diving operations. When water is described as grossly contaminated, that label means the highest level of contamination in this scheme. It signals that conditions are extremely unsafe, requiring maximum precautions, thorough decontamination, or even cancellation of the activity to protect divers.

Keep in mind that other categories indicate progressively lower levels of contamination: heavily contaminated is severe but not as extreme as grossly contaminated; moderately contaminated is less severe; baseline refers to clean or standard conditions. So the category that represents grossly contaminated water is the one described as grossly contaminated—the most severe level in this system. This understanding helps determine when to use enhanced PPE, more extensive decon procedures, or to avoid entering the water altogether.