I saw a gigantic alligator near a swamp in Florida.
The kanji and the word are almost exactly the same. That means they share meanings as well. This word also means mountain stream. Think of it this way, the water for a swamp has to come from somewhere right? It starts out up in the mountains and drains out into a swamp in the valley. The life cycle of a mountain stream into a swamp!
Since this word is made up of a single kanji, it probably uses the kun'yomi reading. You did not learn this reading, so here's a mnemonic to help you to remember: The beginning of the word swamp is actually pretty similar to this word's reading. さわ = "swa"? I'd say it's close enough to make a mnemonic out of in your head.