Definitely I'm not sure =) In Finnish we call them, literally translated, "bog ore" and "lake ore", and as far as I understand they are basically the same stuff. So, I just quickly opened the Finnish wikipedia with "järvimalmi" and then chose the english page to see what name it gives for that type of iron ore. So it might well be that my translation is inaccurate.

I took an another look at Wikipedia, and I think "limonite" is a general name for different types of iron oxides. Some of them are found in bog areas, and some in bottom of lakes. It also says that it regenerates in lakes - once harvested, a same area in lake bottom will regrow a layer of limonite in ten years.