A stream or brook flowing through a valley or mountain area.
谷川のせせらぎが心地よい。
The murmur of the mountain stream is pleasant.
夏になると、谷川で水遊びをする子供たちが多い。
In summer, many children play in the mountain stream.
A mountain stream flows through the hills.
I caught a char in the mountain stream.
I was thirsty, so I drank water from the mountain stream.