The sag was the result of about 600mm of vertigal displacement at pier 22 of the bridge. The investigations found that the displacement of the pier was a result of severe corrosion in the steel piles that support it.

The damage has been attributed to a highly corrosive combination of industrial porous fly ash, high concentrations of chlorides, high sulphate concentrations, low soil resistivity and microbial activity.

All the bridge's piers have been assessed and categorised into three groups covering those requring repairs, monitoring or no further action. The chosen repair  solution involves installation of temporary shoring towers and new, supplemental permanent foundation elements.

Michael Baker Jr and Wiss, Janney, Elstner Associates had joined WisDOT and the US Federal Highway Administration in investigating the problem.