"They are not allowed to swim here."
Translation:Sie dürfen hier nicht schwimmen.
I wonder about this too, whether the nicht could negate the dürfen or the hier, is it's correct translation just on a different emphasis, e.g.
you are not allowed to swim here you are not allowed to swim here
I wouldn't want to report it as accurate response unless the alternative translation makes sense in German!
I can't believe ordering the sentence as Hier duerfen sie nicht schwimmen is wrong. It is 100% correct. The answers need to be more elastic with word order.