Do you say "To swim is dangerous in the river"?
"To swim in the river is dangerous." or
"It's dangerous to swim in the river."
is OK,
but I think "To swim is dangerous in the river."
is a bit strange.

So I'd like to ask if you can move the adverb of the noun clause.

Question

Do you say "To swim is dangerous in the river"?
"To swim in the river is dangerous." or 
"It's dangerous to swim in the river." 
is OK,
but I think "To swim is dangerous in the river."
is a bit strange.

So I'd like to ask if you can move the adverb of the noun clause.

Answer

Your instincts are correct - "to swim is dangerous in the river" is not a natural English sentence.  You can, however, use the gerund "swimming" with that same word order: "Swimming is dangerous in the river."

Answer

"It's dangerous to swim in the river." is the best way to say it in my opinion.
I would change the first one to be "Swimming in the river is dangerous."  The third example does sound a little strange.

Answer

Thank you for the comment:)
sorry in this sentence, I should have said prepositional clause><

Answer

I'd say: "Swimming in the river is dangerous" 
What do you mean by moving the "adverb" of the noun clause?? cause I don't see any adverb..

Nie przegap okazji, by nauczyć się języka w zaciszu własnego domu. Przejrzyj naszą ofertę doświadczonych korepetytorów i zapisz się na pierwszą lekcję już teraz!