swamp:A tract of low-lying ground in which water collects; a piece of wet spongy ground; a marsh or bog. Orig. and in early use only in the N. American colonies, where it denoted a tract of rich soil having a growth of trees and other vegetation, but too moist for cultivation.——Oxford English Dictionary

swamp:land that is always very wet or covered with a layer of water.——Longman Dictionary of Contemporary English  @en