PSM September issue reports no swimming, leaving carl the only one who can swim. The report was 3 pages long (more like 2 with writing) and I quote:
What we do know is that Toni, like the GTA3 guy and Tommy Vercetti before him, will drown if he falls into a large body of water, leaving CJ as the only GTA character who took swimming lessons.
It goes on with other bad news:
But don't try to run inside of a building just because of your aquaphobia --- there are no interior enviroments, just like in GTA3.
It says nothing related to climbing.