Honestly seeing a new part of the sea every day could be fun.

I finally participated in weekly (more or less) winter bathing last year, and even if I stopped, it still was an interesting experience. And I wasn't even paid.
The coldest was 2.5C water and -8C air, and it was painful. Anything over 6 is more or less manageable. And you get a "ohhh, the water is goood" perk for the summer. I mean, for days when water is not actually good, but you've had worse so you enjoy it:)