Since I'm prone to break outs from most sunscreens, I actually use the Mychelle when I swim outdoors (currently only once a week but soon twice a week, 1hr at a time). I don't think it's really meant for swimming, but it does say "reapply after swimming or excessive sweating", so I'm assuming it's at least water resistant to a degree.

I think most sunscreens do need to be reapplied often for it to have proper efficacy.

I only use the Mychelle for my face or it would become very expensive, so I use All-Terrain brand for aqua sports for the rest of my body when I swim. The link I gave you is for land-based sports and I believe this brand also uses mostly natural ingredients, if not all natural. The tubes are pretty small so with the amount I use I won't be able to get the tube to last me the season, but it's pretty cheaply priced. I must put a plug in for iherb.com here as I do all my vitamin and wellness shopping there. Super cheap compared to regular retail stores.