I like the atmosphere and the water color is perfect. It could use some more reference spots for navigating. I think there's a bug where you can never succeed in getting the fish and have to fail and start again (completion bar similar to stardew valley would be nice to have too).
If I had to improve it I would
- make the Amnesia monster instead of a simple timer
- add splash sounds to make it more unnerving and help with finding fishing spots too