what can i say to a girl so that i can start a conversation?

First you need to analyze her actions. Find out what she likes and does. In your case swimming is one thing you know of but find out what her personality is like-that's the most important part because it tells you what kind of an approach you should take. I wouldn't suggest pick up lines because they're stupid and make no sense anyways. All you have to do is walk up to her say hi she says he back then say something about her but don't make it obvious then after that connect it to something else and your already off topic talking about something else. Its not hard. Girls are human beings, they like to talk, most of them don't like starting conversations with guys b/c they're naturally scared to but sometimes that's what they want.

Start it like. Any normal conversation. Something simple like, hello

Well always eazy to start a convo. By saying hello how is your day going? And so on and so on.

I got some popsicles down in the cellar

talk to her like a normal person, after all she is a normal person! just be yourself, thats whats best for both of you :)

Start with like. . .u have very gud figur. .