Watershed is an area of land where all water drains to a common river, lake, or ocean. Rain and melted snow flow across the land into streams and rivers within this area. Watersheds can be small or very large, covering wide regions. Every piece of land is part of a watershed.

Watersheds are found across all land areas on Earth, from mountain regions to flat plains. They include rivers, streams, lakes, and the land that directs water flow. Boundaries between watersheds are often formed by higher land such as hills or ridges.

Watersheds exist as part of Earth’s water system over long periods. They are used to describe how water moves across land in different regions. Many communities, ecosystems, and water systems are connected within a watershed.