Friendly reminder: rescuing a drowning person (even a child) is incredibly dangerous if you have not been trained in how to do it. They
will try to climb on top of you if they get a hold of you and unless you are an exceptionally strong swimmer they will then proceed to drown you. The drowning reflex overrides most people's abilities to process other thoughts, with the result that a loved one is just as likely to drown you as a stranger.
Many people are embarrassed by their inability to swim and so won't mention it in circumstances that you would expect them to -- visits to water parks, beaches, lakes, or even acting jobs that involve being pushed off a dock into a lake (oy). Don't assume that a person can swim, even if they tell you otherwise.