A bikini is a two-piece bathing suit with the upper piece being skimpy and much like a bra. While many pieces have a lower piece that has buttons or a zipper, it is less common to have the upper piece with a zipper. It is advantageous over clip buttons because it is held much more securely in place and is a huge advantage when doing serious swimming in surf.
Find a zipper bikini at a retailer that has a lot of options for swimming. It is cold in the Northern Hemisphere but starting to be perfect swimming weather down here. Tell your friends that better bikinis have landed on the market. They look great, and while the strap in back might be a little thicker, it is perfect for intense swimming even in surf. If your goal is to swim and not just to sunbathe, this could be the solution for you.