Look, this is peak late-90s Disney Channel Original Movie territory—which means it's safe, wholesome, and completely forgettable. The premise (kid turns into a merman on his 13th birthday) has potential, but the execution is hampered by TV-movie budget constraints and a script that never goes deeper than surface-level.
The ratings tell the story: 5.9 on IMDb, 2.8 on Letterboxd, 54% audience score on Rotten Tomatoes. Even people who grew up with this stuff find it hard to revisit. The effects are clunky, the pacing drags, and the emotional beats are predictable Disney formula.
That said, it's harmless. If you have a 7-year-old who's obsessed with mermaids and you need something utterly safe on Disney+, this will do the job without causing any issues. Just don't expect them to ask to rewatch it, and don't expect to stay awake yourself. There are simply better family fantasy movies out there—even from the same era.