The original Waterloo Bridge (1817–1934) was not built by women. It was designed by John Rennie (the Elder), preeminent Scottish civil engineer, and constructed 1811–1817 by contracted labor—including convict labor—under the Strand Bridge Company.
A persistent urban legend claims women built the *replacement* bridge (1942–1945) during WWII while men were at war. Partially true: Peter Lind & Co. employed ~350 women (welders, painters, laborers) on the current box-girder bridge (opened 1945). They were paid less than men; their contribution was unacknowledged for decades. Historian Christine Wall's research (2000s) and a 2015 plaque now recognize them.
So: Original = men (incl. convicts). Replacement = men + women (wartime). The myth attaches to the wrong bridge but honors real women.