汽水

1. Origins, structure, and basic meaning

• Structure: 汽水, read きすい, means brackish water, where fresh water and seawater mix.
• Basic usage: In 河口の汽水には海と川の生物が共に暮らしている。, marine and river organisms live together in brackish water at a river mouth.

2. Common pitfalls and similar expressions

• A name for the water
  • 河口 names the location, while 汽水 describes the mixed water there. As the salinity example shows, the mixture can vary with the tides, so the term does not specify one fixed salt concentration.