[TOMT][CARTOON][2000s] Cartoon About a Weird Town That Had a Mermaid

This might be a bit of a hard one or a lost cause, but here goes:

I've been trying to find this old animation from when I was younger. I must have seen it around 2004, but it was likely made earlier. I distinctly remember seeing it while I was on an airplane.
I was very young when I saw this, but

The clearest memory I have is that the cartoon had a song that played near the beginning. I remember the lyrics to the song were kind of repetitive. It was kind of a back-and-forth type of singing where someone (or perhaps a group) would call out, "don't say it out loud!" and then the response (in a different voice) would say, "Polka Street!"

I don't know if Polka Street was actually what they were saying, but that's what it sounded like to me. It could have very well been "Poker Street" or "Pokka Street" or any other similar sounding phrase.

This music segment served as a kind of intro/opening where various characters were shown. I believe the cartoon was just about some strange happenings in the town (which I assumed to be centered around Polka Street).

A major character was a Mermaid. I don't remember what she was doing, but I remember clips of her sitting on land near the beach, just kind of hanging out. At some point she met this guy and I think he was trying to keep her presence a secret.

Thats all I can really think of ATM. If any more details come to mind, I will be sure to post.