I am fascinated and afraid (at the same time) of whirlpools and water currents.
I wonder if a average human could survive water currents or whirlpools or maybe even the Saltstraumen?
It depends very much on the specific geography. But the idea of "whirlpools" that suck down people or entire ships, never to be seen again (which I suspect is what fascinates you) is largely a myth. The dangers aren't any different (and typically much smaller) than those posed by whitewater rapids in rivers. Specific dangers are:
Yes, you can survive it... if you've got the skills. Not many years ago I watched a film at a mountain film festival, and it was about the first guys to ever kayak the Congo River. They weren't only the first people to kayak the river, they were also the first people to navigate it-and survive.
Here's a clip from National Geographic: https://www.youtube.com/watch?v=HeZjJk2lTHs You basically just do your best to stay upright, point your nose out, lean forward, and paddle like crazy to either try to escape it, or ride it out.
I would say no, because according to records, the strait is not even considered navigable except during short periods of slack tide.
Does that mean a person couldn't survive? No certainly not, but I wouldn't bet my own life to try.
About 60 persons have drowned in Saltstraumen the last 60 years. Only a few of them have been found. If you go down when the stream is going into the Skjerstadfjord (when it is high-water), a boat or a body will be taken down to the bottom of the fjord because of the special geological shape of the underwater landscape. Then you will never come up! The stream is only 20 meters deep over the threshold, and up to 900 meters deep in the fjord inside. The pressure of the water will keep you at the bottom!