遡上

1. Origins, structure, and basic meaning

• Structure: Written 遡上 and read そじょう, it is the upstream movement of fish or other travelers against a river's flow.
• Basic usage: It occurs when fish return to spawn and when a channel beside a dam assists their passage.

2. Common pitfalls and similar expressions

• Against the current, not merely upward
  • The defining direction is from downstream toward upstream along the watercourse.