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Might be Rat-a-Tat. The main character is a mouse rather than a dog, but he looks pretty dog-like to me. There is a mermaid episode, too.
I ran a search on Google and found this French cartoon about a mermaid and a hyena who lives on an island: Zig & Sharko
. Is this the one you are looking for?
Not Rat-a-Tat or Zig & Sharko. I think french either (sorry). Maybe italian or something. Also, I think it had a Protagonist Title
I'm going crazy over this
Tra la la la, tra la la la, Chop the wood to light the fire
Is it possibly Bob's Beach?
It's Polo.
https://www.youtube.com/watch?v=82w6l9ZbhTo
Oh Riz and Sharko is actually pretty funny
@Michael M yes, that's it. thanks a lot. i've been tring to find it for soooo long
Tra la la la, tra la la la, Chop the wood to light the fire
Around 2017, there was this French (I think) TV show on Boomerang in Brazil. It was about a dog boy living in a treehouse in the middle of the sea. He had other friends who were also anthropomorfic animals, one of them being some kind of mouse princess who lives in the clouds and plays a giant organ-thingy.
I clearly remember an episode where Dog Boy goes underwater, meets a mermaid and helps her escape two burglar-looking guys on a submarine.