Ending immunity for lifeguards looks to me like a solution in search of a problem.  How exactly does someone get injured by a lifeguard's bad decision?  If you get into trouble in the water, you're already in peril, and should be thankful there's someone there at all.  How could a lifeguard make it even worse?  Conversely, the potential for unintended consequences, like a lack of people willing to do this work, could actually increase negative outcomes for the average swimmer.