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National assessment of river protection in the United States

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Abstract

To address the enduring and deepening crisis facing fresh waters, many nations have recently set bold targets for freshwater protection. However, the lack of comprehensive databases and integrative frameworks hampers a robust evaluation of current freshwater protections and prioritization of future opportunities to meet these goals. This study provides a comprehensive assessment of river protection for the USA by reconciling the disparate array of major federal, state, tribal and private protection mechanisms into a single, multifaceted index. We report that just over one tenth of the river length of the contiguous USA and less than one fifth of rivers nationwide are currently protected at a level deemed viable. Lowland headwater streams and intermittent watercourses are consistently underprotected. Protection is also often spatially misaligned with other conservation objectives, where only a small fraction of watersheds with high biodiversity, habitat intactness and importance to drinking water supply are adequately (30% of river length) protected. Our assessment of river protection highlights the urgency to increase new and fortify existing protections for rivers in the years to come if we are to meet ambitious conservation targets, reverse the curve of biodiversity loss and ensure that healthy rivers benefit everyone.

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Fig. 1: Extent of river protection in the USA.
Fig. 2: Representativeness of river protection in the USA.
Fig. 3: Interconnectedness of river protection among states.
Fig. 4: Identifying high-priority watersheds to guide future river protection.
Fig. 5: Evaluating watershed protection potential.

Data availability

The data that support the findings of this study are available via Zenodo at https://doi.org/10.5281/zenodo.17279334 (ref. 74). The sources of the datasets are available within the paper (and its Supplementary Information files). To make these data more accessible, we have also created an interactive, online mapping explorer that allows anyone to explore the extent of protection and identify conservation opportunities for US rivers available at https://map.myriver.americanrivers.org/.

Supplementary Information is available for this paper. Correspondence and requests for materials should be addressed to L.C. and J.D.O.

Code availability

The code to reproduce the results and figures of this study is available via GitHub at https://github.com/liseCSP/National-Protected-Rivers-Assessment.

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Acknowledgements

This project was funded by American Rivers. We thank M. Khoury from The Nature Conservancy for the Outstanding Tribal Resource Waters Datasets; D. Hockman-Wert, M. Snyder and R. Flitcroft from the US Forest Service for the Northwest Forest riparian reserve dataset; and all the GIS analysts at various state agencies for the State Wild and Scenic datasets, the Outstanding National and State Resource Waters datasets and the riparian buffer datasets.

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Author notes

  1. These authors contributed equally: Lise Comte, Julian D. Olden.

Authors and Affiliations

  1. Conservation Science Partners, Truckee, CA, USA

    Lise Comte, Julian D. Olden, Caitlin Littlefield & Brett G. Dickson

  2. School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, USA

    Julian D. Olden

  3. American Rivers, Washington, DC, USA

    John Zablocki & David Moryc

Authors

  1. Lise Comte
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  2. Julian D. Olden
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Contributions

Conceptualization, methodology and writing (original draft): L.C. and J.D.O. Data collection, curation and formal analysis: L.C. Funding acquisition: C.L., B.G.D. and D.M. Project administration: J.D.O., C.L. and B.G.D. Writing (review and editing): L.C., J.D.O., C.L., B.G.D., J.Z. and D.M.

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Correspondence to
Lise Comte or Julian D. Olden.

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The authors declare no competing interests.

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Nature Sustainability thanks Lucy Bastin, Matthew Dietz and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Table 1 Contribution of different protection types to total protected river length in the United States (in %)
Full size table

Extended Data Fig. 1 Overview of the workflow and mechanisms of river protection considered in this assessment.

River conservation [blue], riparian and floodplain conservation areas [green], endangered species critical habitat [magenta], terrestrial protected areas (strict) [pink], terrestrial protected areas (other) [beige], multiple use (special management) [dark grey], and multiple use (other) [grey]. Abbreviations: Protected Area Database of the United States (PAD-US), National Conservation Easement Database (NCED), International Union for Conservation of Nature (IUCN), Areas of Critical Concern (ACEC), Inventoried Roadless Areas (IRA), National Parks (NP), Research natural Areas (RNA), State Wilderness Areas (SWA), Wilderness Areas (WA).

Extended Data Fig. 2 Spatial distribution of river protection according to major categories of protection.

The thickness of the river segments is scaled according to stream order. To resolve overlap among mechanisms for display purposes, the colors are shown according to the following hierarchy: ONRW/OTRW > Wild and Scenic Rivers > State Wild and Scenic Rivers > Eligible Wild and Scenic Rivers > Scenic Riverways, National Rivers and Recreation Areas > Riparian and Floodplain Conservation Areas > Northwest Forest Plan – Key Watersheds > Watershed Protection Areas > Fishing Management Areas > IUCN I > IUCN II > IUCN III > IUCN IV > IUCN V > IUCN VI > IUCN OCA > Critical Habitat (ESA) > Multiple use > Riparian Buffers. For the terrestrial protected areas, we adopted the International Union for Nature Protected Areas categories, ranging from strict nature reserves (category I) to other conservation areas (category OCA, also including unassigned protected areas), as opposed to designation types to avoid the difficulty in assigning a specific rank to each designation type separately.

Extended Data Fig. 3 Mechanisms of protection of U.S. rivers.

Network showing the contribution of the individual mechanisms of river protection across the entire U.S. where the size of the circles indicates the total percentage of river length protected by a given mechanism, the thickness of the links the degree of co-occurrence among mechanisms, and the colors the major protection categories (only mechanisms representing > 0.01% of the total river network are shown).

Extended Data Fig. 4 Number of protection mechanism per protection class.

Percentage of river length protected according to different classes of the Protected River Index (PRI) and number of individual mechanisms of protection across stream segments.

Extended Data Fig. 5 Representativeness according to freshwater ecoregions.

Percentage of river length protected according to different classes of the Protected River Index (PRI) (colored sectors; right) within freshwater ecoregions and percentage of total river length across freshwater ecoregions (white sectors; left). The inset illustrates the spatial distribution of the freshwater ecoregions corresponding to numbers in brackets on the barplot labels.

Extended Data Fig. 6 Representativeness according to hydrologic regions.

(a) Percentage of river length protected according to different classes of the Protected River Index (PRI) (colored sectors; right) within hydrologic regions (Hydrologic Unit Code 02) and (b) percentage of total river length across hydrologic regions (white sectors; left). The map in (c) illustrates the spatial distribution of hydrologic regions.

Extended Data Fig. 7 Representativeness according to elevation.

Percentage of river length protected according to different classes of the Protected River Index (PRI) within elevation classes (colored sectors; right) and total river length (white sectors; left) across elevation classes. Lowlands < 200 m; Hills = 200-500 m; Mid-altitude = 500-1,000 m; High mountains = 1,000-2,000 m; Very high mountains ≥ 2,000 m.

Extended Data Fig. 8 In-state versus upstream out-of-state viable protected river length among pairs of states in the U.S.

Self-links in the Sankey plot represent in-state viable protected river length within state borders and between-state links upstream out-of-state viable protected river length in the watersheds upstream of the focal states but within the same river basins. Protected river length for each state is expressed as a percentage of in-state and upstream out-of-state total river length, respectively, and not the amount of water exchanged.

Extended Data Fig. 9 Local versus upstream viable protection.

Percentage of viable protection of watersheds (Hydrologic Unit Code 12; HUC12) in the contiguous U.S. where high versus low protection is defined according to the 30% target. The extent of protection is given separately for source watersheds for which upstream protection cannot be estimated.

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Comte, L., Olden, J.D., Littlefield, C. et al. National assessment of river protection in the United States.
Nat Sustain (2026). https://doi.org/10.1038/s41893-025-01693-8

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