Children's book series. A Dolphin (named Sonar?) and his adventures in the sea with other sea creature friends. Cover: blue or blue-green. Read in 2000's.

[Ichika27]

Sorry if the description is unsure or vague cause it's been so many years since I last saw this series and I was super young back then.

I used to have a set of these children's book about a dolphin named "Sonar", I think. He has other sea creature friends and the stories are about their little adventures in the sea. Each book is a short story of Sonar and his friend's adventure. I remember another dolphin character there but I don't remember the name.

I remember that I answered that it's my favorite book when asked in third grade (that was in the year 2000's) and has had it for longer than that. I think there were 5 books in the box set for it and if I remember correctly, the box and the covers for the books are blue or blue-green. Also, I think it's either a set of hardcover books or one of those cardboard books where each page is made of harder material.

I've been trying to google it and I don't see any book resembling the one I remember. If anyone could help me find it, it'd be nice as I've been trying to remember it exactly for a while now. Thank you for reading.

[Kris]

Ichika27, are these children's picture books (about 32-48 pages) or much longer chapter books?

Are the illustrations: detailed, realistic or cartoon-like, painted watercolors or bold graphics, colorful? Do they remind you of a similar book illustrator?

[Kris]

Are there humans in these stories?

UPDATE: Can we eliminate The Adventures of Manny the Manatee by Anthony Dexter? Here's one book cover on Amazon - https://www.amazon.com/Adventures-Man....

[Ichika27]

The books are short and the illustrations are colorful and I think watercolor-like?

I don't remember if there are any humans in it.

[Rainbowheart]

Ichika, did you rule out Kris's suggestion?

[Ichika27]

Oh, I forgot, sorry. I looked it up and it's the not book I was looking for.