To take the question further: do outdoor pools need to close for lightning? Note that the article mentions 5-10 people die in the US every year from lightning while close to bodies of water. I have looked into this before and struggled to find evidence that people swimming in outdoor pools die at any measurable rate due to lightning (but I don't know the base rate of people swimming in outdoor pools who get out when there is lightning). Put another way: is this a true risk, or an action we take because it seems prudent, even if we don't have the supporting data?