沼

1. Origins, structure, and basic meaning

• Structure: 沼 (ぬま) is a shallow, muddy body of standing water. The examples use actual terrain and a simile.
• Basic usage: A real swamp extends deep in a forest; after rain a road becomes muddy 沼のように.

2. Common pitfalls and similar expressions

• Actual marsh and road compared to one
  • The first is an existing landform; のように makes the second a comparison. The road is not reclassified as a geographical swamp.