Not so.
Most sports reps are designed to be sufficiently water resistant to use for swimming. I regularly swim with AP, Corum, Ebel, Hublot, Patek, Breitling, B+R or Rolex.
They were mostly not water resistant out of the box, but some were. Have them pressure tested first to find out.
When not water proof out of the box that is because the assembly and QC mostly is pretty poor.
It is however true that some reps cannot be water proofed. I have a Cartier Pasha and a Porche Worldtimer which both look like they shoud be, but are not.
Choose a model you like, do a search on that and see if it brings up any issues.
And remember if a member has one which was perfect out of the box that was luck. It does not mean that yours will be OK to swim with unless it passed a test first.
Welcome here!!