Marshland, wetland, or swamp — land that is waterlogged and muddy.
沼地には近寄らないほうが安全だ。
It's safer not to go near a swamp.
子どものころ、沼地で遊んで服を汚した。
As a child I played in the marsh and got my clothes dirty.
開発のために一部の沼地が埋め立てられた。
Some of the marshland was filled in for development.