The Amphawa Floating Market which is said to be one of largest in Thailand is located along a section of the Amphawa canal near Wat Amphawan Chetiyaram in Samut Songkhram which itself is quite a small town (see marked in red within map below).
The Amphawa market has been at this location since at least 1766 during the reign of King Prasat Thong when this area flourished as an agricultural community.