Siuil a run: which version is correct gaelic?

The first song on my mind today was "Down by the Sally Gardens" and then I listened to several different versions of Siuil a run. I'm confused though, because I am hearing so many different pronunciations for Gaelic and I don't know which is correct.

I've heard about 8 different versions and all are singing with different pronunciation. I learned how to sing it in Gaelic, but now that I know it, I'm wondering if my version is even right.

Most of these singers are all Irish, so how are they coming up with so many variations?

I wonder if Gaelic is really hard and fast or people just wing it.