Im a little bit confused where the challenge comes in, I was just swimming from side to side dragging boats.
Other than that the presentation was really nice and clean, the gameplay was also satisfying.
You were probably playing Cozy mode. In that mode, that is all you do. Try timed mode and let me know what you think!
I did play timed mode, are there any other differences than the timer?
Maybe obstacles in the water could add some more, but overall i think the concept is really great!