Definition from Wiktionary, the free dictionary
wetland (plural wetlands)
- Land that is covered mostly with water, with occasional marshy and soggy areas.
2013 January 1, Nancy Langston, “The Fraught History of a Watery World”, American Scientist, volume 101, number 1, page 59:
- European adventurers found themselves within a watery world, a tapestry of streams, channels, wetlands, lakes and lush riparian meadows enriched by floodwaters from the Mississippi River.
land that is covered mostly with water, with occasional marshy and soggy areas
The plural form is more commonly used.