If you ever want people to think you’re insane, simply describe, in as much detail as you can remember, the plot of “Ponyo.” Like most of the films from Hayao Miyazaki, Japan’s beloved animation master, it’s beautiful to look at, bizarre to contemplate, and so imaginative that it’s hard to believe it was conceived by a rational human being. And who knows, maybe it wasn’t.

It can’t match Miyazaki’s masterpiece, “Spirited Away,” for sheer creative brilliance, but “Ponyo” is whimsical and delightful in its own ways, and geared toward a much younger audience. Apparently inspired by “The Little Mermaid,” it’s set in a small harbor town where 5-year-old Sosuke (voice of Frankie Jonas) lives with his mom (Tina Fey) and dad (Matt Damon), although the latter, a ship’s captain, is usually out at sea. On the shore, Sosuke finds a freakish fish with a human face stuck in a bottle, rescues her, and puts her in a bucket. He calls her Ponyo. Everyone refers to her as a “goldfish” even though she is not gold and barely looks like a fish.

Ponyo (voice of Noah Cyrus) is the offspring of Fujimoto (Liam Neeson), a human who somehow lives under the sea now, and Gran Mamare (Cate Blanchett), the goddess of the ocean (or something). That explains why Ponyo has a fish body and human face, at least insofar as anything is really “explained” in a Miyazaki movie. After being brought back to the ocean by Fujimoto’s minions, Ponyo gets into her dad’s magic cave and turns herself into a human so she can hurry back and be friends with Sosuke. “Mom!” Sosuke exclaims. “Ponyo came back, and she’s a little girl now!” Mom takes this in stride.

Suddenly, the moon is coming too close to the Earth, upsetting the tides and causing the water level to rise. Ponyo uses her magic to make a toy boat into a full-sized sailing vessel. (When Ponyo uses her magic, her feet and hands turn into those of a chicken. I do not know why.) Ponyo and Sosuke play games and eat ham. Ponyo loves ham. Fujimoto is angry. Ponyo’s little fish sisters become huge but still fishy. I think Ponyo and Sosuke save the world, or at least the town. There are three old ladies with the voices of Cloris Leachman, Betty White, and Lily Tomlin. One of them, hearing of Ponyo’s healing abilities, says, “I’d let a fish lick me if it would get me out of this wheelchair!” If I wanted to, I could recite a hundred more amusing and fanciful details.

Yet the strangest thing about the film is that despite all the obvious creativity, it’s overlong and occasionally dull. The beautiful colors and images are constant, but the story sometimes stalls for several minutes at a time before reviving with another burst of glorious weirdness. The wizards at Pixar idolize Miyazaki, and this is something they have in common with him: Even a lesser work of theirs is better than many other people’s best. “Ponyo” can’t measure up to “Spirited Away,” but it has more than enough joy and laughter to outweigh its less-than-inspired moments.

B (1 hr., 40 min.; G, with some very mild thematic elements.)