My friends use the Apple watch for windsurfing and wing foiling. They say its really good. I plan to take my Galaxy Active 2 out for my next windsurf session and test it out.
I have used it for windsurfing for a year, and no problem with water. I am not satisfied with speed tracking though, as I don trust it quite, I think maybe it doesnt refreshes often enough to get correct speed, as I can keep a high speed for quite a while, but afterwards in the samsung health app it appears as a spike. It shows my rides well tracked on the map, so that is very cool.