I swim twice a week in a sports complex. My hours are late and the place is almost empty.
A few days ago a guy started a chat with me while I was in the sauna. I saw nothing wrong with it, so I maintained the small talk, but then the guy asked me out.
I said I wasn't interested, but he wouldn't take "no" for an answer, though I told him no at least ten times. He also asked me for my phone number. Not wanting to give him a fake one I said "not interested, thanks" another time and escaped to the swimming pool. The guy followed me there.
He almost gave me a heart attack when he groped me in the water. What's more, the guy who swam in our lane told us off (probably thinking we were a couple) to take it somewhere else, then swam off, annoyed.
Other than him there was only the lifeguard (in quite a distance) and a few other swimmers.
As I couldn't get rid of the guy I escaped to the changing rooms and waited there for him to leave.
What should I do if I encounter him next time? Tell the lifeguard? But his job is to rescue people from the water, not from sexual harassment?
Environment: western, liberal