Watershed Diagram Labeled – Divide, Tributaries, Outlet

All 11 parts on the diagram

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Start here: 5 main parts 5

Watershed All the land whose streams and rain drain to one outlet. It is also called a drainage basin or catchment.
Drainage divide The ridges and hills that separate one watershed from the next. Rain on one side drains into this watershed, rain on the other into its neighbour.
Main river The largest stream in the watershed. Every other stream flows into it on its way to the outlet.
Tributaries The smaller streams that flow into the main river.
Outlet The one point all the watershed's water leaves by. For example, a river mouth or the outflow of a reservoir.

On the land: 3 3

Smaller watershed The land drained by one tributary. Larger watersheds are made of many smaller ones.
Reservoir A lake held back on the main river. Lakes and reservoirs are part of the watershed's surface water.
Wetland Marshy ground by a stream, part of the watershed's surface water.

Where the water comes from: 3 3

Precipitation Rain and snow falling on the watershed. It is where the watershed's water comes from.
Runoff Rain that runs over the ground instead of soaking in. It goes down the slopes to the stream.
Groundwater Water that has soaked into the ground. It seeps slowly to the stream, which is why a stream can keep flowing when it has not rained.

How this list was compiled: Read 2026-09-27. U.S. Geological Survey, Water Science School, Watersheds and Drainage Basins, https://www.usgs.gov/water-science-school/science/watersheds-and-drainage-basins : a watershed is an area of land that drains all the streams and rainfall to a common outlet, such as the outflow of a reservoir, the mouth of a bay or any point along a stream channel; also called a drainage basin or catchment; the ridges and hills that separate two watersheds are the drainage divide; it takes in surface water (lakes, streams, reservoirs and wetlands) and the underlying groundwater; larger watersheds contain many smaller watersheds; precipitation, runoff and infiltration; a stream often keeps flowing where there is no direct runoff from recent rain. Licence: own work

The drawing: Drawn for this site by script, 2026-09-27. Own work, nothing traced. Licence: own work

How it works

A watershed diagram labeled twice: from above like a map, then in a slice across the valley. Start with the 5 main parts, then the land, then where the water comes from.

Read the full guide

From above

Trace the dashed divide along the ridges: every drop that lands inside it ends up at the outlet. Tributaries feed the main river, and each tributary drains its own smaller watershed.

In the slice

Rain falls on both slopes of the valley. Some runs off down to the stream; some soaks in and becomes groundwater, which seeps to the stream long after the rain stops.

Pick any point on the map and follow the water downhill: if it reaches the outlet, that point is inside the watershed.

Questions and answers

What is a watershed?

An area of land that drains all its streams and rainfall to one outlet, such as a river mouth or the outflow of a reservoir. It is also called a drainage basin or catchment.

What is a drainage divide?

The ridges and hills that separate one watershed from the next. Rain falling on either side of a divide ends up in a different watershed.

Is groundwater part of a watershed?

Yes. A watershed takes in its surface water, meaning streams, lakes, reservoirs and wetlands, and all the groundwater underneath.