If I wanted to swim from here {the pacific northwest} to china what would prevent me from doing so?

If you're planning to take the north route (ie. via Canada, Alaska, Russia...) then things that would hinder your quest: Canadian/US/Russian coast guards, extremely icy water, lack of food...

If you're planning to take the south routh (ie. via Hawaii) then thing that would hinder your quest: US coast guards, shark-invested waters, lack of food...

In order to survive the swim, you'll need professional gear to keep you from the cold and protect you from the sharks. You'll also need to setup rest points along the way so you can refuel and recharge your body.

One better way is to get one of those inflatable boats, stock up on power bars, water and Gravol and row yourself to China...

Besides the fact that a person cannot physically swim that far. there are sharks, underwater volcanoes, pirates, the water is too cold, etc. oh and when you got to china you would probably be arrested by the government. other than hat you're good to go.

Common sense? Do you really think you could swim 5275 miles ( the distance from Seattle to Shanghai.)

Charles Darwin award winner!

I Would Say Lack Of Food, Drinking Water, Crazy Sharks, Nasty Waves, All That Salt Water Eating You Away, And Last But Not Least Getting Ran Over By Ships.

your endurane is not strong enough, lack of stamina, cold water, hunger, thirst, etc

Well I think the biggest threat would be from sharks.

But then you would still need a visa to enter visa as well as your support crew.

Hahahaha, cool . good one , i'm going to purpose to on my next bypass to. inspite of each and every thing this is in basic terms a hundred sixty five km. If I swim fairly rapid ,non stop , i ought to in all probability do it in a pair of days........ and save the boat fare too.

Well obviously if you asked this, seems nothing would prevent you.

But for most people, their common sense would prevent them from attempting to swim thousands of miles across the Pacific ocean.

Nothing! but before you start, just try swim 10 laps in any olympic size pool... and then you'll see how practical it is..
good luck