清流

1. Origins, structure, and basic meaning

• Structure: 清流 (せいりゅう) is a compound noun for a stream whose flowing water is notably clear.
• Basic usage: 清流で手を洗う makes the mountain stream the place of an action, while 清流を守る makes the clean water environment the object preserved by removing riverbank trash.

2. Common pitfalls and similar expressions

• Place of use and object of conservation
  • 清流で marks the place where water is used, while 清流を marks what conservation affects. The second does not mean physically holding a stream; it means preserving its clean condition.