Nya?

According to The Wiggles, "nya" is a noise naturally associated with swimming and all things aquatic:
"We're swimming / swimming at the pool/ Let's go swimming / water's oh-so cool ...

... Nya-nya! Nya-nya-nya-nya nya-nya!
Nya na-na-na-na-na-na na!
Nya-nya-nya-nya nya-nya! / Nya-nya-nya-nya!"

I don't get the connection either. Maybe it's an Aussie thing. (And yes, I watched the Wiggles' DVD with subtitles so I could be correct about the lyrics).