If you go out from a cave and there is water and you need to swim there are 2 problems:
The first one is the loading. I run a gtx970 and ive got 16 gbs of ram, so thats not the problem. IF you go out the cave the loading will take like 2 or 3 seconds, while you will keep loosing stamina.
The second one is even worse. IF you jump to the cliff next to the cave to avoid drowning, once you have climbed it you need to walk like 2 more tiles or you keep loosing stamina and sinking. So its like the 2 first tiles after you separate yourself to the "edge that dont allow u to pick things". You should repair that