**Spoiler Free Solution**
When given control of Laura, the game's secondary protagonist, during the beginning of chapter two, you'll find yourself talking to Gorf.
You'll discuss a pair of glasses, which will lead to the addition of a second hotspot by the swamp - not the one directly behind Gorf.
By this hotspot is another one you can use to gain a reed; then use this reed on the swamp next to it.
Achievement unlocked!