"Around the Bay of Mont St. Michel is polder land ? farmland reclaimed by Normans in the 19th century with the help of Dutch engineers"

Several of the elements making up the site are related to Polders e.g "Engineers' dike through the Haarlemmermeer polder The large Haarlemmermeer polder was split into two by an engineers' dike about 15 kilometres from the centre of Amsterdam. Built between 1890 and 1895 it is 10.5 kilometres long and it allowed the southern half of the polder to be inundated while the remaining half stayed dry." And "Fort near Hoofddorp In the middle of the Haarlemmermeer polder and the Engineers' dike, this fort was built between 1903 and 1904. Because of limited space and the depth of the polder, a two level bomb proof building was built with a deep moat and a special machine gun post to cover the deep moat."

"The Alblasserwaard is a polder in the province South Holland in the Netherlands. It is mainly known for the windmills of Kinderdijk, a village in the northwest of the Alblasserwaard." Wiki

Schokland lost its status as an island when the Noordoostpolder was reclaimed from the sea in 1942.

an exceptionally well preserved polder landscape that is unique in North America (AB ev)

Poldered parts of the Po Delta are situated within the inscribed area (Wiki cites the "Delta of the river Po such as Bonifica Valle del Mezzano" in its list of Polders.)

Signifcant parts of the inscribed area (and even more of the uninscribed areas!) have been "poldered" (ref AB eval and map)