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mountain river; mountain stream
清らかな山川で釣った。
I fished in the clear mountain stream.
夏でも山川の水は冷たい。
Even in summer, the water of the mountain stream is cold.
昔はこの山川にたくさんのイワナが生息していたそうだ。
I heard that many iwana trout used to inhabit this mountain stream.