noun
river water
Refers to water in rivers, often used in environmental, engineering, or hydrological contexts.
河川水の水質調査を行った。
We conducted a water quality survey of the river water.
Means 'seawater', contrasting with 河川水 which is fresh river water.
Compound of 河川 (kasen, 'rivers') and 水 (sui, 'water').