noun
Refers to a stream in a mountain or hilly area, often with a sense of a small valley or ravine. The word evokes a natural, scenic watercourse.
沢のせせらぎが心地よい。
The murmur of the mountain stream is pleasant.
この沢には小さな魚がたくさんいる。
There are many small fish in this mountain stream.
noun
Refers to a low-lying, waterlogged area such as a swamp or marsh. This sense is less common than the 'mountain stream' meaning and may appear in place names or descriptive contexts.
その沢には珍しい植物が生えている。
Rare plants grow in that marsh.
The kanji 沢 originally means 'marsh' or 'swamp' in Chinese, and in Japanese it has extended to mean a mountain stream or valley, likely due to the association of water in such landscapes. The reading さわ is a native Japanese word (kun'yomi).