I agree with your general point but I think some of the assumptions you've made aren't quite accurate: > They have also been staring at the same pool for hours

I agree with your general point but I think some of the assumptions you've made aren't quite accurate: > They have also been staring at the same pool for hours and their brain is ignoring all the visual noise that is distracting you. I'd suspect mental fatigue would counteract any benefits you'd get from increased filtering. Which, I assume, is why life guards are generally rotated regularly. > They also have the benefit of stereo vision and sound. Sound might not be of much help here because drowning is usually something that happens quietly (as the linked site also explains).