No, not mouth-to-mouth, but I did rescue, on two separate, occasions', girls' at School when I saw them on the bottom of the swimming pool!
One of those times, I dove in fully dressed, sans shoes!
Got them out of the pool, & applied the Holger-Nielsen method of resuscitation on them. They were ok, as speed of rescue was the main thing.
The School Nurse ironed all my clothes' dry, whilst I had a shower, then wrapped in a glorious heavy cotton bathrobe, until clothes were ready!
If I can remember correctly, at that time, I was 16 yo, & was the youngest person in the State to hold a Lifesaving Award of Merit, & Instructor's Badge.