HydrionisGlobal Water Intelligence
Monitored reservoir

Anderson Ranch Reservoir

Anderson Ranch Reservoir is a federal reservoir operated by the United States Bureau of Reclamation in its Pacific Northwest region, with published operating records from 1950.

Storage recordAnderson Ranch Reservoir, Dam, and Powerplant (AND)

Storage now, against this reservoir's own record

333.87 Mm³
Stored, August 2026
26th
Percentile among 78 Augs on record
+0.9%
Against the Aug 1991–2020 average
-3.3%
Change over the 12 months to 2026-08

Storage in August 2026 was lower than most Augs on record, ranked against 78 other Augs held for this reservoir.

Storage, 1946–2026

Monthly mean storage
936 monthly values, 1946 to 2026
Monthly mean storageMonthly mean storage: Anderson Ranch Reservoir in Mm³, from 1946.4166666666667 to 2026.5833333333333.0200400600Mm³1946.41666666666671957.91666666666671967.66666666666671977.41666666666671987.16666666666671997.41666666666672007.16666666666672016.9166666666667Year

Monthly means of the publisher's daily record. Volume, not percentage of capacity — see below for why.

What the shaded periods are (0 events)

Not shown on this chart

  • The 1976 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
  • The 2022 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
  • Yorkshire drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
  • Cantareira water crisis, São Paulo — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
  • Cape Town Day Zero — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
  • European drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
View the data behind this chart
240 of 936 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 936 would be longer than this page and unusable with a screen reader.
PeriodAnderson Ranch Reservoir (Mm³)
June 194624.6
June 1947118
March 194837.4
July 1948104
February 194946.4
July 194985.6
February 195066.7
June 1950269
October 1950258
February 1951329
June 1951508
October 1951353
February 1952148
June 1952512
October 1952282
February 1953218
June 1953512
October 1953310
January 1954238
May 1954457
September 1954349
January 1955239
May 1955311
September 1955325
January 1956243
May 1956443
September 1956457
January 1957300
May 1957428
August 1957433
December 1957348
April 1958223
August 1958432
December 1958359
April 1959388
August 1959435
December 1959437
April 1960473
August 1960412
December 1960262
March 1961181
July 1961259
November 196168.6
March 196260.4
July 1962514
November 1962418
March 1963380
July 1963518
November 1963427
March 1964300
July 1964509
November 1964385
February 1965405
June 1965484
October 1965483
February 1966449
June 1966513
October 1966284
February 1967198
June 1967479
October 1967402
February 1968345
June 1968449
September 1968312
January 1969225
May 1969396
September 1969427
January 1970376
May 1970379
September 1970462
January 1971407
May 1971359
September 1971515
January 1972399
April 1972348
August 1972504
December 1972438
April 1973384
August 1973400
December 1973321
April 1974265
August 1974469
December 1974396
April 1975306
August 1975465
December 1975413
March 1976310
July 1976494
November 1976422
March 1977407
July 1977244
November 197772.4
March 1978106
July 1978516
November 1978424
March 1979394
July 1979457
October 1979273
February 1980260
June 1980522
October 1980351
February 1981356
June 1981521
October 1981398
February 1982355
June 1982508
October 1982463
February 1983382
June 1983525
September 1983516
January 1984321
May 1984387
September 1984439
January 1985340
May 1985495
September 1985310
January 1986322
May 1986498
September 1986420
January 1987405
April 1987441
August 1987188
December 1987111
April 1988140
August 1988163
December 1988116
April 1989201
August 1989375
December 1989278
April 1990302
August 1990233
November 1990183
March 1991165
July 1991222
November 199157.6
March 199248.1
July 199238.7
May 1993243
September 1993412
January 1994362
May 1994350
September 199447.4
January 199518.2
April 1995142
August 1995486
December 1995461
April 1996337
August 1996477
December 1996444
April 1997135
August 1997478
December 1997477
April 1998390
August 1998449
November 1998425
March 1999330
July 1999505
November 1999402
March 2000391
July 2000455
November 2000298
March 2001296
July 2001130
November 200157.5
March 200243.2
July 2002325
October 2002136
February 2003129
June 2003439
October 2003302
February 2004288
June 2004437
October 2004231
February 2005216
June 2005428
October 2005245
February 2006248
May 2006462
September 2006332
January 2007334
May 2007460
September 2007154
January 2008141
May 2008265
September 2008299
January 2009278
May 2009415
September 2009333
December 2009329
April 2010351
August 2010388
December 2010347
April 2011385
August 2011437
December 2011414
April 2012447
August 2012358
December 2012287
April 2013320
August 2013166
November 2013122
March 2014153
July 2014458
November 2014258
March 2015340
July 2015401
November 2015248
March 2016274
July 2016420
November 2016269
March 2017338
June 2017503
October 2017371
February 2018404
June 2018497
October 2018294
February 2019288
June 2019502
October 2019346
February 2020343
June 2020438
October 2020300
January 2021291
May 2021363
September 2021183
January 2022173
May 2022284
September 2022391
January 2023378
May 2023451
September 2023430
January 2024432
May 2024489
September 2024353
December 2024333
April 2025389
August 2025345
December 2025304
April 2026434
August 2026334

The reservoir's year

Seasonal storage profile
Each calendar month's reference average, against the most recent year
Seasonal storage profileSeasonal storage profile: 1991–2020 average, Most recent 12 months in Mm³, from 1 to 12.0200400Mm³123456789101112Month1991–2020 average 1: 281 Mm³1991–2020 average 2: 277 Mm³1991–2020 average 3: 273 Mm³1991–2020 average 4: 291 Mm³1991–2020 average 5: 369 Mm³1991–2020 average 6: 437 Mm³1991–2020 average 7: 407 Mm³1991–2020 average 8: 331 Mm³1991–2020 average 9: 286 Mm³1991–2020 average 10: 285 Mm³1991–2020 average 11: 283 Mm³1991–2020 average 12: 284 Mm³Most recent 12 months 1: 331 Mm³Most recent 12 months 2: 340 Mm³Most recent 12 months 3: 360 Mm³Most recent 12 months 4: 434 Mm³Most recent 12 months 5: 500 Mm³Most recent 12 months 6: 487 Mm³Most recent 12 months 7: 415 Mm³Most recent 12 months 8: 334 Mm³Most recent 12 months 9: 304 Mm³Most recent 12 months 10: 297 Mm³Most recent 12 months 11: 297 Mm³Most recent 12 months 12: 304 Mm³
  • 1991–2020 average
  • Most recent 12 months

Twelve separate averages, one per calendar month. A January average describes Januaries only. Months are plotted 1–12.

View the data behind this chart
Underlying data
Period1991–2020 average (Mm³)Most recent 12 months (Mm³)
Jan281331
Feb277340
Mar273360
Apr291434
May369500
Jun437487
Jul407415
Aug331334
Sep286304
Oct285297
Nov283297
Dec284304

Why this page shows a volume and not a percentage

Water level

Monthly mean water surface elevation
572 monthly values
Monthly mean water surface elevationMonthly mean water surface elevation: Anderson Ranch Reservoir in m, from 1950.75 to 2026.5833333333333.1,2201,2401,2601,280m1950.751985199119972003200920152021Year

An elevation above a datum, not a depth of water and not a distance below the crest. Levels at different reservoirs are measured against different datums and must not be read against one another; this line is comparable only with its own history. Elevation and volume are not proportional either — a metre near the bottom of a reservoir holds far less water than a metre near the top, because the surface area grows with height.

What the shaded periods are (0 events)

Not shown on this chart

  • The 1976 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
  • The 2022 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
  • Yorkshire drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
  • Cantareira water crisis, São Paulo — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
  • Cape Town Day Zero — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
  • European drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
View the data behind this chart
240 of 572 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 572 would be longer than this page and unusable with a screen reader.
PeriodAnderson Ranch Reservoir (m)
1950.751,262
1950.91666666666671,267
1951.16666666666671,268
1951.33333333333331,276
1951.58333333333331,277
19801,262
1980.16666666666671,263
1980.41666666666671,279
1980.58333333333331,275
1980.83333333333331,269
19811,269
1981.16666666666671,271
1981.41666666666671,279
1981.58333333333331,275
1981.751,272
19821,273
1982.16666666666671,265
1982.41666666666671,278
1982.58333333333331,277
1982.751,276
19831,273
1983.16666666666671,268
1983.41666666666671,279
1983.58333333333331,279
1983.751,279
19841,267
1984.16666666666671,264
1984.41666666666671,278
1984.58333333333331,278
1984.751,271
19851,268
1985.16666666666671,268
1985.33333333333331,277
1985.58333333333331,269
1985.751,266
19861,267
1986.16666666666671,272
1986.33333333333331,278
1986.58333333333331,278
1986.751,272
19871,272
1987.16666666666671,273
1987.33333333333331,276
1987.58333333333331,256
1987.751,250
19881,248
1988.16666666666671,248
1988.33333333333331,258
1988.58333333333331,254
1988.751,250
1988.91666666666671,249
1989.16666666666671,250
1989.33333333333331,271
1989.58333333333331,270
1989.751,264
1989.91666666666671,264
1990.16666666666671,263
1990.33333333333331,269
1990.58333333333331,260
1990.751,257
1990.91666666666671,255
1991.16666666666671,254
1991.33333333333331,256
1991.58333333333331,251
1991.751,243
1991.91666666666671,241
1992.16666666666671,240
1992.33333333333331,246
1992.51,239
1992.751,230
1992.91666666666671,226
1993.16666666666671,224
1993.33333333333331,260
1993.51,278
1993.751,271
1993.91666666666671,270
1994.16666666666671,269
1994.33333333333331,269
1994.51,259
1994.751,238
1994.91666666666671,236
1995.16666666666671,242
1995.33333333333331,265
1995.51,279
1995.751,275
1995.91666666666671,276
1996.08333333333331,275
1996.33333333333331,271
1996.51,278
1996.751,274
1996.91666666666671,275
1997.08333333333331,269
1997.33333333333331,268
1997.51,278
1997.751,276
1997.91666666666671,277
1998.08333333333331,276
1998.33333333333331,277
1998.51,278
1998.751,273
1998.91666666666671,274
1999.08333333333331,274
1999.33333333333331,269
1999.51,278
1999.66666666666671,272
1999.91666666666671,272
2000.08333333333331,273
2000.33333333333331,276
2000.51,275
2000.66666666666671,266
2000.91666666666671,266
2001.08333333333331,266
2001.33333333333331,262
2001.51,251
2001.66666666666671,245
2001.91666666666671,241
2002.08333333333331,240
2002.33333333333331,260
2002.51,268
2002.66666666666671,254
2002.91666666666671,251
2003.08333333333331,251
2003.251,256
2003.51,276
2003.66666666666671,268
2003.91666666666671,266
2004.08333333333331,265
2004.251,271
2004.51,271
2004.66666666666671,262
2004.91666666666671,260
2005.08333333333331,260
2005.251,261
2005.51,272
2005.66666666666671,263
2005.91666666666671,261
2006.08333333333331,262
2006.251,266
2006.51,277
2006.66666666666671,268
2006.83333333333331,268
2007.08333333333331,269
2007.251,273
2007.51,270
2007.66666666666671,254
2007.83333333333331,253
2008.08333333333331,253
2008.251,254
2008.51,277
2008.66666666666671,266
2008.83333333333331,265
2009.08333333333331,265
2009.251,267
2009.51,277
2009.66666666666671,269
2009.83333333333331,268
2010.08333333333331,268
2010.251,270
2010.41666666666671,278
2010.66666666666671,270
2010.83333333333331,269
2011.08333333333331,270
2011.251,272
2011.41666666666671,275
2011.66666666666671,273
2011.83333333333331,274
2012.08333333333331,274
2012.251,276
2012.41666666666671,279
2012.66666666666671,265
2012.83333333333331,265
2013.08333333333331,265
2013.251,268
2013.41666666666671,269
2013.66666666666671,251
2013.83333333333331,251
20141,250
2014.251,260
2014.41666666666671,278
2014.66666666666671,264
2014.83333333333331,263
20151,264
2015.251,272
2015.41666666666671,277
2015.66666666666671,263
2015.83333333333331,262
20161,262
2016.251,272
2016.41666666666671,278
2016.66666666666671,264
2016.83333333333331,264
20171,264
2017.251,276
2017.41666666666671,279
2017.58333333333331,273
2017.83333333333331,272
20181,273
2018.251,276
2018.41666666666671,278
2018.58333333333331,269
2018.83333333333331,266
20191,265
2019.251,271
2019.41666666666671,279
2019.58333333333331,274
2019.83333333333331,269
20201,269
2020.251,271
2020.41666666666671,275
2020.58333333333331,269
2020.83333333333331,266
20211,266
2021.16666666666671,266
2021.41666666666671,269
2021.58333333333331,260
2021.83333333333331,256
20221,256
2022.16666666666671,256
2022.41666666666671,275
2022.58333333333331,274
2022.83333333333331,271
20231,271
2023.16666666666671,271
2023.41666666666671,278
2023.58333333333331,276
2023.83333333333331,275
20241,275
2024.16666666666671,275
2024.41666666666671,278
2024.58333333333331,272
2024.751,269
20251,268
2025.16666666666671,269
2025.41666666666671,278
2025.58333333333331,269
2025.751,266
20261,268
2026.16666666666671,270
2026.41666666666671,278
2026.58333333333331,269

Rate and persistence

-0.96 Mm³
Mean drawdown per month over 12 months
0 of 24
Recent months below the 20th percentile for their own month

Rates are computed only across an unbroken run of months, so a rate is never divided by a period in which some of the change was not observed. Percentile counts compare each month with the same calendar month in every other year held.

Location

Anderson Ranch Reservoir
Gauge location
Anderson Ranch ReservoirAnderson Ranch Reservoir — 333.87 Mm³Anderson Ranch Reservoir — 333.87 Mm³

About this data

About this data

Everything below is a property of the data rather than a rating of it. There is deliberately no single confidence score: how much a gap matters depends on what you are about to do with the series, and only you know that.

Source
United States Bureau of Reclamation — Reservoir operations and Colorado River data · US Government work — public domain
How the values came to existMeasured
Period held1946–2026
Completeness96.3% of the periods in that span are held. Gaps are drawn as breaks and never interpolated.
Known gaps
  • Storage is a managed quantity. A falling line can be a rule curve, a scheduled release or a transfer to another system rather than a shortage of water, and nothing here distinguishes them.
  • No capacity figure on a stated basis is held for this reservoir, so no percentage of capacity is computed.
Continuity96% of the months between 1946 and 2026 are held. Monthly means of the publisher's own daily record.
Last read from the publisher2026-09-01
RedistributionPermitted by the upstream licences
Commercial reusePermitted by the upstream licences. No Hydrionis access tier can widen this.
MethodologyHow this was produced

Use this data

Use this data

No bulk download is offered here, which is a licence position rather than a product one: at least one contributing publisher does not permit redistribution. The values can be read on the page, cited, and pointed to at source.

Attribution and citation

Suggested citation for Hydrionis

Hydrionis (2026), Anderson Ranch Reservoir reservoir records, accessed 2026-09-02, hydrionis.com/reservoirs/reservoir-usbr-3641/

Cite Hydrionis where you rely on the compilation, the normalisation, the eligibility judgements or a chart. Where you use an unmodified published value, the publisher’s attribution is the one that is required; crediting Hydrionis as well is welcome and is not something Hydrionis can require of you.

Recommended, not required. Hydrionis does not claim rights over unmodified public data it relayed, and doing arithmetic on somebody else’s measurements does not make them Hydrionis’s. Cite the version and the access date: the Anderson Ranch Reservoir record changes as publishers release and as methods are revised, and a citation without both cannot be checked later. Full guidance is on cite and reuse.

None of the contributing licences requires attribution. Crediting the publishers is still good practice and they are listed above.

Where this comes from

936 monthly observations 1946–2026 Mm³
Spatially aggregatedHigh confidenceAugust 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 129152. Licence: Open.

Method: Monthly mean of the daily values published by the Bureau of Reclamation in acre-feet, converted to Mm³. Months with fewer than 20 days of record are not published rather than averaged from a partial month.

Stored as a volume and not as a share of capacity: the operator publishes what is in the reservoir but not what it holds when full, so a percentage cannot be computed without inventing the denominator.

Retrieved 1 September 2026.

Monthly mean of the daily values published by the Bureau of Reclamation in acre-feet, converted to Mm³. Months with fewer than 20 days of record are not published rather than averaged from a partial month.

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