A lake can be unsafe for people to swim in yet have a healthy ecosystem and vice versa. Or, if your reading is correct, redundancy might be an aesthetic choice.
Interpreting "healthy" as "healthy ecosystem" doesn't really make sense in the context of an initiative focused on people being able to swim.
This thread gives me the vibes of arguing for the sake of arguing. The first point mentions "safe" and "healthy", of course this initiative cares about both good water quality and safety from drowning, because those are quite important things for people wanting to swim.
I was very obviously only making a joke. But ironically your reply perfectly embodies the petty, joyless and argumentative side of HN commenting I was alluding to.
