What two factors can affect a lifeguard's ability to scan the water?

The correct choice highlights how weather and surf conditions can significantly impact a lifeguard's ability to effectively scan the water. Adverse weather, such as rain or fog, can reduce visibility, making it challenging for lifeguards to spot swimmers in distress or other hazards. Similarly, surf conditions, including wave height and frequency, can further complicate the scanning process; for example, large waves may obscure the view of swimmers or create dangerous situations that require immediate attention.

While other factors might influence a lifeguard's overall effectiveness, they are not as directly impactful on the visual scanning process compared to weather and surf conditions. Sunlight can create glare, affecting visibility, while crowd size can make it harder to focus on individual swimmers, but these are secondary to the more immediate effects of weather and surf conditions. Therefore, understanding the primary role of those two factors is critical for maintaining safety and vigilance while on duty.