I love the gameplay loop of this game - going through a seemingly ordinary level, then finding new puzzles and secrets each time is a really engrossing experience. The lazy river is a great tie-in to the theme as well. Unfortunately, I only ever found two of the trophies (I saw a little cave by the end of the river, but couldn’t find a way in for the life of me!), but I bet if I played it again I’d discover more.
You mentioned on your itch page that you hoped to add more things to find, so I won’t bring that up as a suggestion. However, another improvement you could make would be improving the movement and feel. At the moment, the motion of the river is a bit janky, and you can move so fast through it that it doesn’t feel all that lazy. It’d be nice to have a smoother ride with more time to look for secrets.
Note: there are a few places you can get stuck, which forces you to reset the game. I would put some sort of failsafe in so player don’t lose their progress from getting snagged on a ring.