I have a pair and I would say they are water resistant. I would not wear them in the water, but if they get splashed a little, or you are on a boat, and get a little wet, that wouldn't hurt them.
If you are talking about Nike Straprunner II's I would say they are waterproof. I have a pair and they did fine getting soaked however, the rough patterned tread were kind of hard on my feet once they got wet.