The middle set of spans has a plaque for Lassig Bridge & Iron Works dated 1898, so I'm listing that as the build date, another set of spans shows the spot where a plaque SHOULD be, and the area looks to fit the footprint of that of the Lassig plaque (but I'd like your second opinion on that.).
The third set of spans had a Wisconsin Bridge & Iron Co. "plaque." (it's more of a tab), so either a derailment or flooding caused the loss of that set of spans, because I' say they are younger than the other two sets of spans.