Photo taken from NPS.gov
View this photo at nps.gov
BH Photo #278012
This is the remnant of the change bridge.
The listing ought to be "Change Bridge" not "Chain Bridge". If the website continues to cite it as "Chain Bridge" it sustains the misconception that chains were in some way involved. It is very common locally to mispronounce the name - I think this is maybe because the locals no longer understand why the canal changed from one side of the river to the other.
The dam which facilitated the change was called "Chain Dam" locally. That is a completely different subject - probably the source of the confusion. The dam is now gone - bridgefolks don't need to perpetuate the error about the name of the bridge.