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Idaho reservoir levels

1.41 million acre-feet

Water stored in Idaho's 21 major federal reservoirs, October 19, 2026 (provisional)

21.9% of active capacity; 54.9% of the 1991–2020 average for October 19; −28.7% from October 19, 2025 (1,981,828 acre-feet).

Source: U.S. Bureau of Reclamation, Pacific Northwest Hydromet, reservoir storage. Data period October 19, 2026. Status: provisional.

Reservoir by reservoir

How full each reservoir was on October 19, 2026, as a share of its active capacity. The tick marks its 1991–2020 average for October 19, so a fill short of the tick is below normal for the season. Percent of capacity covers the 17 reservoirs Reclamation prints a capacity for; the average covers the 20 that reported every year from 1991 to 2020. These are Reclamation's provisional daily readings as of this site's last refresh, not a live feed.

Percent of active capacity

  1. American Falls10%
  2. Palisades8%
  3. Jackson Lake (Wyo.)9%
  4. Lake Cascade56%
  5. Anderson Ranch56%
  6. Arrowrock29%
  7. Lucky Peak16%
  8. Deadwood46%
  9. Lake Lowell71%
  10. Island Park22%
  11. Lake Walcott16%
  12. Ririe29%
  13. Little Wood22%
  14. Grassy Lake (Wyo.)46%
  15. Mann Creek1%
  16. Reservoir A29%
  17. Soldiers Meadow23%

Source: U.S. Bureau of Reclamation, Pacific Northwest Hydromet, reservoir storage. Data period October 19, 2026. Status: provisional.

Capacity: Reclamation's May 2013 Monthly Reservoir Status Report. Average computed by Understand Idaho from the daily archive.
Data table (21 rows)
ReservoirOctober 19, 2026 (acre-feet)Active capacity (acre-feet)Percent full1991–2020 average for October 19 (acre-feet)Percent of averageOctober 19, 2025 (acre-feet)
American Falls159,4741,672,6009.5%391,77140.7%164,571
Palisades98,7051,200,0008.2%488,11620.2%82,986
Jackson Lake (Wyo.)74,525847,0008.8%490,72615.2%550,848
Lake Cascade360,267646,46055.7%382,99794.1%373,859
Anderson Ranch230,370413,10055.8%222,437103.6%240,461
Arrowrock80,030272,20029.4%75,333106.2%83,258
Lucky Peak42,107264,40015.9%52,96379.5%44,417
Deadwood73,987161,90045.7%84,23387.8%75,502
Lake Lowell112,560159,37070.6%85,983130.9%114,197
Island Park29,856135,20022.1%72,26041.3%54,344
Lake Walcott15,16395,20015.9%48,81731.1%27,660
Ririe23,20980,50028.8%41,23856.3%43,153
Little Wood6,61430,00022.0%6,99594.6%4,273
Grassy Lake (Wyo.)6,96815,20045.8%11,30861.6%9,832
Mann Creek5911,1000.5%55210.7%178
Reservoir A8693,00029.0%1,04383.3%776
Soldiers Meadow5442,37023.0%75572.1%547
Henrys Lake66,181n/an/a76,62286.4%77,886
Black Canyon23,492n/an/a27,65485.0%23,564
Payette Lake7,600n/an/a9,97276.2%8,600
Lake Waha1,155n/an/an/an/a916

Not drawn, because Reclamation prints no capacity for them: Henrys Lake (66,181 acre-feet), Black Canyon (23,492 acre-feet), Payette Lake (7,600 acre-feet), Lake Waha (1,155 acre-feet).

At the close of each water year

Contents on 30 September summed across every reservoir the dataset lists except Lake Waha, for the years in which all of the rest report; earlier years, when fewer of the dams existed, are not summed. Lake Waha (about 932 acre-feet, 0.05% of statewide storage) is left out because it does not report for several stretches the other reservoirs do, including 1995 through 2003.

Change and comparison

From 1988 (1.01 million acre-feet) to 2026 (1.37 million acre-feet), the change was +34.9%.

The series high is 4,433,748 acre-feet in 1997 and the low is 961,826 acre-feet in 1992.

The largest category in storage by reservoir is Cascade Dam and Lake Cascade at Cascade, Idaho at 359,686 acre-feet; next is Anderson Ranch Dam and Reservoir at 234,624 acre-feet.

Historical data

Idaho reservoir levels, 1988 to 2026Idaho reservoir levels, 1988 to 2026. Idaho: 1,014,345.9 in 1988, 1,368,786 in 2026.02M4M6M20002020IdahoAcre-feetIdaho reservoir levels, 1988 to 2026Idaho reservoir levels, 1988 to 2026. Idaho: 1,014,345.9 in 1988, 1,368,786 in 2026.02M4M6M1990200020102020IdahoAcre-feetIdaho reservoir levels, 1988 to 2026Idaho reservoir levels, 1988 to 2026. Idaho: 1,014,345.9 in 1988, 1,368,786 in 2026.02M4M6M1990200020102020IdahoAcre-feet

Source: U.S. Bureau of Reclamation, Total reservoir storage (computed by Understand Idaho).

Data table (39 rows)
PeriodIdaho (acre-feet)
19881,014,345.9
19892,381,162.8
19901,748,847.1
19912,161,596.7
1992961,825.5
19933,656,441.3
19941,045,160.3
19954,069,964.6
19963,984,528.1
19974,433,747.7
19984,013,028.9
19993,842,483.3
20002,271,826.9
2001987,438.8
20021,269,954.0
20031,329,230.8
20041,376,025.0
20052,003,011.9
20062,826,971.5
20071,263,157.8
20082,629,017.5
20093,321,482.2
20102,924,715.3
20114,050,976.3
20122,130,892.2
20131,243,071.8
20142,697,806.3
20152,128,316.9
20161,885,961.6
20174,129,194.0
20182,923,520.8
20193,121,344.2
20202,938,868.0
20211,317,620.2
20221,586,082.0
20232,969,313.0
20242,744,547.0
20251,920,529.0
20261,368,786.0

Storage by reservoir

This breakdown is from U.S. Bureau of Reclamation, on a different basis than the headline figure above. Reservoir contents on 30 September each year, from Reclamation's Hydromet daily archive.

Acre-feet

  1. Cascade Dam and Lake Cascade at Cascade, Idaho359,686.0
  2. Anderson Ranch Dam and Reservoir234,624.0
  3. Palisades Reservoir near Irwin, ID129,608.0
  4. Lake Lowell at Lower Embankment near Caldwell, ID114,197.0
  5. American Falls Reservoir at American Falls, ID90,032.0
  6. Deadwood Dam, Idaho72,134.0
  7. Arrowrock Dam and Reservoir70,273.0
  8. Henrys Lake Dam and Lake on Henrys Fork nr. Lake, ID65,691.0
  9. Jackson Lake at Dam on Snake River near Moran, WY63,942.0
  10. Lucky Peak Lake near Boise, ID43,397.0
  11. Black Canyon Dam and Reservoir near Emmett, ID29,610.0
  12. Ririe Dam and Lake near Ririe, ID23,634.0
  13. Island Park Dam and Reservoir, ID20,361.0
  14. Minidoka Dam and Lake Walcott, ID18,327.0
  15. Payette Lake at McCall, Idaho18,200.0
  16. Grassy Lake near Moran, WY6,797.0
  17. Little Wood Dam and Reservoir near Carey, ID6,533.0
  18. Lake Waha near Lewiston, ID1,164.5
  19. Reservoir A Near Lewiston Orchards, ID1,048.0
  20. Soldiers Meadow Reservoir634.0
  21. Mann Creek Dam and Reservoir nr Weiser, ID58.0

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

Data table (21 rows)
Reservoir2026 (acre feet)
Cascade Dam and Lake Cascade at Cascade, Idaho359,686.0
Anderson Ranch Dam and Reservoir234,624.0
Palisades Reservoir near Irwin, ID129,608.0
Lake Lowell at Lower Embankment near Caldwell, ID114,197.0
American Falls Reservoir at American Falls, ID90,032.0
Deadwood Dam, Idaho72,134.0
Arrowrock Dam and Reservoir70,273.0
Henrys Lake Dam and Lake on Henrys Fork nr. Lake, ID65,691.0
Jackson Lake at Dam on Snake River near Moran, WY63,942.0
Lucky Peak Lake near Boise, ID43,397.0
Black Canyon Dam and Reservoir near Emmett, ID29,610.0
Ririe Dam and Lake near Ririe, ID23,634.0
Island Park Dam and Reservoir, ID20,361.0
Minidoka Dam and Lake Walcott, ID18,327.0
Payette Lake at McCall, Idaho18,200.0
Grassy Lake near Moran, WY6,797.0
Little Wood Dam and Reservoir near Carey, ID6,533.0
Lake Waha near Lewiston, ID1,164.5
Reservoir A Near Lewiston Orchards, ID1,048.0
Soldiers Meadow Reservoir634.0
Mann Creek Dam and Reservoir nr Weiser, ID58.0
  • 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.

Percent of active capacity

20.9% in 2026 (estimate). 30 September storage summed across the reservoirs with a published active capacity, divided by the sum of those capacities, times 100, for the years in which all of those reservoirs report. Every year's storage is divided by the capacity printed in Reclamation's May 2013 Monthly Reservoir Status Report, the only edition still served, because capacity changes only rarely; 17 of the 21 reservoirs the dataset lists carry a capacity figure, and four (Black Canyon, Henrys Lake, Payette Lake and Lake Waha) are excluded because no capacity is printed for them.

Percent of active capacity, 1978 to 2026Percent of active capacity, 1978 to 2026. Reservoir storage as a percent of active capacity: 66.0% in 1978, 20.9% in 2026.0.0%20.0%40.0%60.0%80.0%198020002020Reservoirstorage asa percentof activecapacityPercentPercent of active capacity, 1978 to 2026Percent of active capacity, 1978 to 2026. Reservoir storage as a percent of active capacity: 66.0% in 1978, 20.9% in 2026.0.0%20.0%40.0%60.0%80.0%198020002020Reservoirstorage as apercent ofactivecapacityPercentPercent of active capacity, 1978 to 2026Percent of active capacity, 1978 to 2026. Reservoir storage as a percent of active capacity: 66.0% in 1978, 20.9% in 2026.0.0%20.0%40.0%60.0%80.0%19801990200020102020Reservoirstorage as apercent ofactive capacityPercent

Source: U.S. Bureau of Reclamation, Reservoir storage as a percent of active capacity (computed by Understand Idaho).

Data table (49 rows)
PeriodReservoir storage as a percent of active capacity (percent)
197866.0%
197933.2%
198057.3%
198133.8%
198273.8%
198371.7%
198471.8%
198539.9%
198662.7%
198722.5%
198815.1%
198937.5%
199027.0%
199134.0%
199214.4%
199358.6%
199415.5%
199565.4%
199664.2%
199771.5%
199864.5%
199961.6%
200035.6%
200114.9%
200219.3%
200320.3%
200421.1%
200531.2%
200644.8%
200719.0%
200841.5%
200953.0%
201046.5%
201165.2%
201233.2%
201318.7%
201442.6%
201533.3%
201629.3%
201766.5%
201846.5%
201949.7%
202046.8%
202119.9%
202224.4%
202347.2%
202443.6%
202529.9%
202620.9%

Source

Organization
U.S. Bureau of Reclamation
Dataset
Total reservoir storage (computed by Understand Idaho)
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)
Original file
https://www.usbr.gov/pn-bin/daily.pl
License
Public domain. U.S. federal government work.
Our copy
Total reservoir storage (computed by Understand Idaho)

Caveats

  • Computed by Understand Idaho from Pacific Northwest Hydromet, reservoir storage; it is not a figure the publisher releases.

Inputs: Pacific Northwest Hydromet, reservoir storage.

Percent of active capacity:

Organization
U.S. Bureau of Reclamation
Dataset
Reservoir storage as a percent of active capacity (computed by Understand Idaho)
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)
Original file
https://www.usbr.gov/pn-bin/daily.pl
License
Public domain. U.S. federal government work.
Our copy
Reservoir storage as a percent of active capacity (computed by Understand Idaho)

Inputs: Pacific Northwest Hydromet, reservoir storage.

Cite

Cite this page as Understand Idaho, “Idaho reservoir levels”, https://understandidaho.com/water/reservoirs/, retrieved on the date you read it, and the publisher named above for the figures themselves. The dataset behind it is described in the data catalog.

This page was last updated .