Most tourists call it “The Japanese Bridge,” but its not Japanese at all. I suspect some call it that for its resemblance to the covered Japanese bridge in Hoi An.
In fact, the original bridge was built in 1776 by a lady of the village who had the good fortune to marry a wealthy mandarin. Taking pity on her former neighbors, Trân Thị Đạo built the bridge with her own money so they would not have to wade or ferry themselves across the small creek. However, she also wanted a son, and building the bridge was part of her prayers. Another local legend has it that she indeed had a son who fell deathly ill at the age of sixteen. The illness was traced to the ghost of a young girl who had died before she married and had children, and being unfilled, her spirit fell in love with the young boy, inhabited his body and made him ill. To this day, some local people make offerings to the girl at the small shrine in the middle of the bridge. Regardless of which of the two stories you believe, it is recorded that her good deed brought great fortune to the village. The King noticed her virtue, and in November 1776, proclaimed that from henceforth, the villagers were exempt from being drafted into either the army or doing forced labor for the government.
The bridge was severely damaged by typhoons in 1844 and 1904 and rebuilt each time, and restore
in 1954 and again in 1971. Today it’s a great place to sit on the benches that span the length of the bridge. enjoy some conversation, and watch Việt Nam go by.
The village used to be named Thanh Toàn, hence the name of the bridge. The 
name was changed to Thủy Toàn some time ago, but near the edge of the village is a shrine dedicated to venerating Trân Thị Đạo - - the lady of the bridge.
(My thanks to Steve Boswell for the information about the bridge and its builder.)