Which indicator suggests that the water clarity or quality is good?

The indicator that suggests the water clarity or quality is good is the visibility of the pool bottom and racing lines. When the bottom of the pool is clear and the racing lines are easily seen, it typically indicates that the water has been well-maintained, free from algae, dirt, and other contaminants that can compromise water quality. Clear visibility allows for better safety and monitoring of swimmers, as it ensures that coaches and lifeguards can easily spot any issues or emergencies that may arise in the water. Additionally, good visibility is essential for athletes to gauge their positions and improve their performance during races.

The other options, while relevant to the comfort and safety of swimmers, do not directly measure water clarity or quality. Temperature, absence of debris, and swimmer reports of feeling safe can indicate a pleasant swimming environment, but they do not specifically reflect the visual clarity and cleanliness of the water itself.