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

295.48 Mm³
Stored, September 2026
28th
Percentile among 77 Seps on record
+3.4%
Against the Sep 1991–2020 average
-2.7%
Change over the 12 months to 2026-09

Storage in September 2026 was lower than most Seps on record, ranked against 77 other Seps held for this reservoir.

Storage, 1946–2026

Monthly mean storage
937 monthly values, 1946 to 2026
Monthly mean storageMonthly mean storage: Anderson Ranch Reservoir in Mm³, from 1946.4166666666667 to 2026.6666666666667.0200400600Mm³1946.416666666666719581967.83333333333331977.66666666666671987.51997.83333333333332007.66666666666672017.5Year

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 937 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 937 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
September 1957393
December 1957348
April 1958223
August 1958432
December 1958359
April 1959388
August 1959435
December 1959437
April 1960473
August 1960412
December 1960262
April 1961215
August 1961197
November 196168.6
March 196260.4
July 1962514
November 1962418
March 1963380
July 1963518
November 1963427
March 1964300
July 1964509
November 1964385
March 1965288
July 1965523
October 1965483
February 1966449
June 1966513
October 1966284
February 1967198
June 1967479
October 1967402
February 1968345
June 1968449
October 1968254
February 1969230
June 1969519
September 1969427
January 1970376
May 1970379
September 1970462
January 1971407
May 1971359
September 1971515
January 1972399
May 1972336
September 1972485
January 1973381
May 1973435
August 1973400
December 1973321
April 1974265
August 1974469
December 1974396
April 1975306
August 1975465
December 1975413
April 1976350
August 1976436
December 1976424
April 1977415
July 1977244
November 197772.4
March 1978106
July 1978516
November 1978424
March 1979394
July 1979457
November 1979265
March 1980269
July 1980513
November 1980350
March 1981377
June 1981521
October 1981398
February 1982355
June 1982508
October 1982463
February 1983382
June 1983525
October 1983520
February 1984271
June 1984508
October 1984376
February 1985326
May 1985495
September 1985310
January 1986322
May 1986498
September 1986420
January 1987405
May 1987459
September 1987134
January 1988106
May 1988202
September 1988136
January 1989113
April 1989201
August 1989375
December 1989278
April 1990302
August 1990233
December 1990176
April 1991164
August 1991131
December 199152.8
April 199259.0
August 199220.3
June 1993473
September 1993412
January 1994362
May 1994350
September 199447.4
January 199518.2
May 1995304
September 1995465
January 1996466
May 1996383
September 1996457
January 1997469
May 1997350
August 1997478
December 1997477
April 1998390
August 1998449
December 1998430
April 1999249
August 1999437
December 1999406
April 2000373
August 2000360
December 2000297
April 2001284
July 2001130
November 200157.5
March 200243.2
July 2002325
November 2002130
March 2003137
July 2003451
November 2003295
March 2004302
July 2004371
November 2004229
March 2005218
June 2005428
October 2005245
February 2006248
June 2006506
October 2006330
February 2007335
June 2007453
October 2007142
February 2008140
June 2008445
October 2008281
February 2009277
May 2009415
September 2009333
January 2010329
May 2010423
September 2010348
January 2011353
May 2011404
September 2011409
January 2012417
May 2012485
September 2012283
January 2013287
April 2013320
August 2013166
December 2013121
April 2014216
August 2014365
December 2014265
April 2015392
August 2015301
December 2015241
April 2016391
August 2016320
December 2016268
March 2017338
July 2017484
November 2017379
March 2018415
July 2018434
November 2018292
March 2019293
July 2019475
November 2019345
March 2020346
July 2020407
November 2020296
February 2021289
June 2021339
October 2021173
February 2022172
June 2022433
October 2022381
February 2023377
June 2023496
October 2023428
February 2024436
June 2024501
October 2024341
January 2025331
May 2025469
September 2025304
January 2026331
May 2026500
September 2026295

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: 333 Mm³Most recent 12 months 9: 295 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
Aug331333
Sep286295
Oct285297
Nov283297
Dec284304

Why this page shows a volume and not a percentage

Water level

Monthly mean water surface elevation
573 monthly values
Monthly mean water surface elevationMonthly mean water surface elevation: Anderson Ranch Reservoir in m, from 1950.75 to 2026.6666666666667.1,2201,2401,2601,280m1950.751985199119972003200920152021Year

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 573 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 573 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
1981.83333333333331,272
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
1985.41666666666671,279
1985.58333333333331,269
1985.751,266
19861,267
1986.16666666666671,272
1986.41666666666671,279
1986.58333333333331,278
1986.751,272
19871,272
1987.16666666666671,273
1987.41666666666671,272
1987.58333333333331,256
1987.751,250
19881,248
1988.16666666666671,248
1988.33333333333331,258
1988.58333333333331,254
1988.751,250
19891,249
1989.16666666666671,250
1989.33333333333331,271
1989.58333333333331,270
1989.751,264
19901,263
1990.16666666666671,263
1990.33333333333331,269
1990.58333333333331,260
1990.751,257
19911,255
1991.16666666666671,254
1991.33333333333331,256
1991.58333333333331,251
1991.751,243
19921,240
1992.16666666666671,240
1992.33333333333331,246
1992.58333333333331,235
1992.751,230
19931,224
1993.16666666666671,224
1993.33333333333331,260
1993.58333333333331,274
1993.751,271
1993.91666666666671,270
1994.16666666666671,269
1994.33333333333331,269
1994.58333333333331,248
1994.751,238
1994.91666666666671,236
1995.16666666666671,242
1995.33333333333331,265
1995.58333333333331,277
1995.751,275
1995.91666666666671,276
1996.16666666666671,271
1996.33333333333331,271
1996.58333333333331,277
1996.751,274
1996.91666666666671,275
1997.16666666666671,256
1997.33333333333331,268
1997.58333333333331,277
1997.751,276
1997.91666666666671,277
1998.16666666666671,274
1998.33333333333331,277
1998.58333333333331,275
1998.751,273
1998.91666666666671,274
1999.16666666666671,267
1999.33333333333331,269
1999.58333333333331,274
1999.751,272
1999.91666666666671,272
2000.16666666666671,271
2000.33333333333331,276
2000.51,275
2000.751,266
2000.91666666666671,266
2001.16666666666671,266
2001.33333333333331,262
2001.51,251
2001.751,243
2001.91666666666671,241
2002.16666666666671,240
2002.33333333333331,260
2002.51,268
2002.751,252
2002.91666666666671,251
2003.16666666666671,252
2003.33333333333331,263
2003.51,276
2003.751,266
2003.91666666666671,266
2004.16666666666671,266
2004.33333333333331,275
2004.51,271
2004.751,261
2004.91666666666671,260
2005.16666666666671,260
2005.33333333333331,266
2005.51,272
2005.751,262
2005.91666666666671,261
2006.08333333333331,262
2006.33333333333331,276
2006.51,277
2006.751,268
2006.91666666666671,269
2007.08333333333331,269
2007.33333333333331,276
2007.51,270
2007.751,253
2007.91666666666671,253
2008.08333333333331,253
2008.33333333333331,263
2008.51,277
2008.751,265
2008.91666666666671,265
2009.08333333333331,265
2009.33333333333331,274
2009.51,277
2009.751,268
2009.91666666666671,268
2010.08333333333331,268
2010.33333333333331,274
2010.51,277
2010.751,269
2010.91666666666671,269
2011.08333333333331,270
2011.33333333333331,273
2011.51,278
2011.751,273
2011.91666666666671,274
2012.08333333333331,274
2012.33333333333331,278
2012.51,276
2012.66666666666671,265
2012.91666666666671,265
2013.08333333333331,265
2013.33333333333331,269
2013.51,263
2013.66666666666671,251
2013.91666666666671,251
2014.08333333333331,250
2014.33333333333331,269
2014.51,276
2014.66666666666671,264
2014.91666666666671,264
2015.08333333333331,266
2015.33333333333331,276
2015.51,273
2015.66666666666671,263
2015.91666666666671,262
2016.08333333333331,262
2016.33333333333331,278
2016.51,274
2016.66666666666671,264
2016.91666666666671,264
2017.08333333333331,265
2017.33333333333331,277
2017.51,278
2017.66666666666671,271
2017.91666666666671,272
2018.08333333333331,273
2018.251,276
2018.51,275
2018.66666666666671,266
2018.91666666666671,265
2019.08333333333331,265
2019.251,271
2019.51,277
2019.66666666666671,271
2019.91666666666671,269
2020.08333333333331,269
2020.251,271
2020.51,273
2020.66666666666671,267
2020.91666666666671,266
2021.08333333333331,265
2021.251,268
2021.51,264
2021.66666666666671,257
2021.91666666666671,256
2022.08333333333331,256
2022.251,260
2022.51,277
2022.66666666666671,272
2022.91666666666671,271
2023.08333333333331,271
2023.251,272
2023.51,278
2023.66666666666671,275
2023.83333333333331,275
2024.08333333333331,275
2024.251,277
2024.51,276
2024.66666666666671,270
2024.83333333333331,269
2025.08333333333331,268
2025.251,272
2025.51,274
2025.66666666666671,266
2025.83333333333331,266
2026.08333333333331,269
2026.251,275
2026.51,274
2026.66666666666671,266

Rate and persistence

-0.69 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 — 295.48 Mm³Anderson Ranch Reservoir — 295.48 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
Completeness96.4% 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 publisher2026-10-01
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 2026-10-05, 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

937 monthly observations 1946–2026 Mm³
Spatially aggregatedHigh confidenceSeptember 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 October 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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