Do you have to keep your face out of the water, too?

Yup! I've never, ever managed to deal with putting my face in the water when I swim.

The excellent thing is that with outdoor swimming, it's quite a sensible way to swim anyway: I'm happy to swim in the Serpentine (as long as I get a bath afterwards to wash the algae out of awkward places), but I wouldn't want to drink it. Also, I am not kidding about the swan.