What should be done immediately if a swimmer accidentally defecates in the pool?

When a swimmer accidentally defecates in the pool, the immediate response should be to close the pool and superchlorinate. This is crucial because fecal matter can introduce harmful pathogens into the water, making it unsafe for other swimmers. Superchlorination involves adding a higher concentration of chlorine to the pool, which effectively kills bacteria and viruses that could pose health risks.

This process goes beyond simply maintaining normal chlorine levels; it ensures that any contaminants are dealt with promptly and effectively, minimizing the risk of waterborne illnesses.

While closing the pool is an important first step for safety and to begin proper remediation, superchlorination specifically addresses the contamination from fecal matter. The other options, such as raising the pH or adding clarifier, do not directly target the immediate health risks associated with fecal contamination and are therefore not suitable responses to such an incident.