In rivers and hydrology, the main stem is defined as the principal channel within a given drainage basin, into which all of the tributary streams in a drainage basin flow. Viewed in terms of the Strahler stream order system, the main stem would be the highest order stream amongst the streams in a given drainage basin. In rivers that anabranch or braid, the main stem is defined as the channel or thread of the channel that carries the majority of the flow, though sometimes there is no dominant channel.

The United States National Weather Service considers the main stem as the principal object of flood forecasting.

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General bibliographic references

• Cushing, Colbert E., Benke, Arthur C., Rivers of North America

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