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Idaho reservoir storage

Daily storage, read on the newest day every reservoir reports and on 30 September each year, and active (usable) storage capacity, for the Bureau of Reclamation reservoirs on the Snake, Boise, Payette, Weiser, and Clearwater systems that serve Idaho irrigation, plus Jackson Lake and Grassy Lake in Wyoming, which are administered as upstream Snake River System storage for Idaho delivery.

Figures

Acre-feet

  1. Cascade Dam and Lake Cascade at Cascade, Idaho359,686
  2. Anderson Ranch Dam and Reservoir234,624
  3. Palisades Reservoir near Irwin, ID129,608
  4. Lake Lowell at Lower Embankment near Caldwell, ID114,197
  5. American Falls Reservoir at American Falls, ID90,032
  6. Deadwood Dam, Idaho72,134
  7. Arrowrock Dam and Reservoir70,273
  8. Henrys Lake Dam and Lake on Henrys Fork nr. Lake, ID65,691
  9. Jackson Lake at Dam on Snake River near Moran, WY63,942
  10. Lucky Peak Lake near Boise, ID43,397
  11. Black Canyon Dam and Reservoir near Emmett, ID29,610
  12. Ririe Dam and Lake near Ririe, ID23,634
  13. Island Park Dam and Reservoir, ID20,361
  14. Minidoka Dam and Lake Walcott, ID18,327
  15. Payette Lake at McCall, Idaho18,200

Source: U.S. Bureau of Reclamation, Pacific Northwest Hydromet, reservoir storage. Data period 2026.

Pages built on this dataset

Publisher

Organization
U.S. Bureau of Reclamation
Publisher’s dataset
Pacific Northwest Hydromet, reservoir storage
File or API used
https://www.usbr.gov/pn-bin/daily.pl
Methodology
https://www.usbr.gov/pn/hydromet/station.js

Coverage

Geography
Idaho (statewide; two of the 21 reservoirs, Jackson Lake and Grassy Lake, are physically sited in Wyoming)
Time coverage
1910-2026 (30 September storage, varies by station); the newest daily reading and the same day a year earlier (latest storage); 2013 (capacity)
Update frequency
Daily at the publisher (latest storage, refreshed here every two weeks or sooner); annual (30 September storage); irregular (capacity, revised only after events such as a sedimentation survey)
Retrieved
October 20, 2026
License of the records
Public domain. U.S. federal government work.
Rows
1,625 observations, 1910-2026

Measures

MeasureWhat it measuresUnit
Reservoir storageReservoir contents on 30 September each year, from Reclamation's Hydromet daily archive.acre feet
Latest reservoir storageReservoir contents on the newest day every reservoir has reported, and on the same calendar day a year earlier, from Reclamation's Hydromet daily archive.acre feet
Average storage for the date, 1991-2020The mean of a reservoir's 1991-2020 daily readings on the same calendar day as the latest storage, for reservoirs that reported all 30 years. Computed by Understand Idaho from Reclamation's Hydromet daily archive.acre feet
Reservoir active capacityActive (usable) storage capacity, from Reclamation Pacific Northwest Region's Monthly Reservoir Status Report.acre feet

Caveats

  • Storage is read on 30 September, the approximate close of Idaho's irrigation season, and is provisional Hydromet data subject to revision.
  • The latest storage is as current as this site's last refresh of the data, not a live reading; the page names the day it is from. The average for that date is computed by Understand Idaho from the 1991-2020 daily readings, for the reservoirs that reported all 30 years, and is not a figure Reclamation publishes in this form.
  • Active capacity figures come from Reclamation's May 2013 Monthly Reservoir Status Report, the only edition still served; capacity changes only rarely.
  • Active capacity has no figure for four of the 21 reservoirs: Black Canyon, Henrys Lake, Payette Lake and Lake Waha.
  • Jackson Lake and Grassy Lake sit in Wyoming but are included as upstream Snake River System storage released for delivery to Idaho irrigators.
  • Magic Reservoir is grouped with these systems in general reporting but is a State of Idaho project, not Reclamation's, and is not included.
  • Hydromet publishes some storage readings below zero, meaning the water stood below the level Reclamation counts contents from; they are carried as published. Anderson Ranch (1946 to 1949) and Lake Cascade (1948 and 1949) read negative while the reservoirs first filled, and Mann Creek read -224 acre-feet on 30 September 2013, after a dry summer drew it down from about 3,000 acre-feet in early August.
  • Storage is stored to one decimal acre-foot as published; capacity is converted from the report's thousand-acre-foot column to acre-feet.

How to cite

Understand Idaho, “Pacific Northwest Hydromet, reservoir storage”, compiled from U.S. Bureau of Reclamation, Pacific Northwest Hydromet, reservoir storage. Retrieved October 20, 2026. https://understandidaho.com/data/usbr-reservoirs/.

Cite U.S. Bureau of Reclamation directly for the figures themselves.

This page was last updated .