No. I have collected my ore from river. In Finland the ore have been mainly collected from waters, as its easy to find and collect it from there, and there is lots of rivers and lakes where to search from.
Ahh. Here in the States there are lots of swampy areas with iron in them. You can tell because the water will often have an odd sheen in certain parts, like oil on water. I don't know what it is about the iron that makes this, but it's almost always a sign you can find ore there.