There is construction activity suggesting that replacement of this bridge is underway.
The causeway on the west end is being widened, with the new fill being added on the south side of the causeway.
It appears the plan is to make the causeway 4 lanes, build a new 2 lane bridge on the south side of the existing bridge and then after the new bridge is finished traffic would go over the new bridge and the old one would be replaced, making the finished project a 4 lane causeway and bridge. There isn't (yet) any evidence of widening Highway 51 on either end of the project.
I will try and get a picture or two of the new causeway construction and post it later.