Wat Pet, or the Monastery of the Duck, was situated on the city island on the edge of the Ayutthaya Historical Park in the Pratu Chai Sub-district. At present, two restored chedis are still visible on the west side of Chikun Road, and thus the temple must have stood along the west bank of Khlong Pratu Khao Pluak (1). This canal has been filled up except for a minimal water stretch on the premises of Wat Racha Praditsathan.
On a 19th-century map, by an unknown surveyor, Wat Pet features farther from the Pratu Khao Pluak Canal, southeast of Wat Lat (2) and north of Wat Pa Kup (defunct). Phraya Boran Rachathanin puts in this position Wat Khok Muang. Wat Pet is here indicated with a chedi.
Phraya Boran Rachathanin indicates Wat Pet on his 1926 CE map, Wat Pet on the east bank of Khlong Pratu Khao Pluak, north of Thewa Sathan (a Brahmin shrine part of Wat Sao Ching Cha) and west of Wat Pa Kup. Phraya Boran (1871-1936 CE) was the Superintendent Commissioner of Monthon Ayutthaya from 1925 till 1929 CE but occupied important functions since 1896 CE in Monthon Ayutthaya.
On both 19th and begin-20th century maps, the monastery is located on the east side of the former Khlong Pratu Khao Pluak.
On a map of the Fine Arts Department drafted in 1993 CE, Wat Pet is curiously indicated on the opposite side of the canal.
It is evident that there were different monastic structures in this area, and their denomination remains, unfortunately, a bit of guesswork.
I added Wat Pet under the Historical Park sub-section on this website until I have tangible evidence that the temple needs to be filed under the Historical City sub-section.
Historical data about Wat Pet and its construction are not known.
Wat Pet was in geographical coordinates: 14° 21' 19.1" N, 100° 34' 07.2" E.
Footnotes:
(1) Khlong Pratu Khao Pluak, or the ‘Canal of the Gate of Unmilled Rice’, was part of a waterway running through the middle of Ayutthaya from north to south. The canal, a shortcut in the oxbow of the Lopburi River, ran until the Chikun Bridge and continued to the Chinese water gate (Pratu Jin). It was filled up somewhere in the early 20th century.
(2) On the 19th-century map, a bridge over Khlong Pratu Khao Pluak is visible near Wat Lat - see the webpage "The bridges along Khlong Pratu Khao Pluak - Pratu Jin.”