Mainstem Rivers of the Conterminous United States (ver. 3.0, February 2026)

Mainstem rivers serve as the backbone of a connected network of hydrologic units that cover the landscape. A mainstem connects a headwater source area to an outlet.

The series of data releases, Mainstem Rivers of the Conterminous United States, referred to as "Mainstems", identifies the same mainstem paths across spatial scales in hydrographic datasets for the United States.

This data release, Mainstems V3, builds on the preceding Mainstems data release: Mainstem Rivers of the Conterminous United States ver. 2.0, referred to as Mainstems V2, https://doi.org/10.5066/P92U7ZUT. V3 has improved network connectivity and includes two additional hydrographic datasets and two additional hydrologic unit datasets.

Concepts and background for understanding this data release can be found in the following two publications. Users of these data are strongly encouraged to review them in addition to the data quality and entity and attribute sections of this metadata.

1) Mainstems: A logical data model implementing mainstem and drainage basin feature types based on WaterML2 Part 3: HY Features concepts, https://doi.org/10.1016/j.envsoft.2020.104927
2) Generating a reference flow network with improved connectivity to support durable data integration and reproducibility in the coterminous US, https://doi.org/10.1016/j.envsoft.2023.105726

A graphical representation of mainstem and drainage basin concepts showing how a mainstem relates to flowlines and hydrologic locations like stream gages can be found here. https://www.sciencebase.gov/catalog/file/get/65cbc0b3d34ef4b119cb37e9?name=mainstem_schematic.png

For more information about the data contents of Mainstems V3 see the supplemental information, data quality, and entity and attribute section of this metadata record.

First release: August 2022
Revised: February 2023 (ver. 2.0)
Revised: February 2026 (ver. 3.0)