HydrionisGlobal Water Intelligence
Monitored reservoir

Lake Granby

Lake Granby is a federal reservoir operated by the United States Bureau of Reclamation in its Great Plains region, with published operating records from 1985.

Storage recordLake Granby and Dam

Storage now, against this reservoir's own record

389.40 Mm³
Stored, August 2026
13th
Percentile among 68 Augs on record
-30.7%
Against the Aug 1991–2020 average
-36.1%
Change over the 12 months to 2026-08

Storage in August 2026 was lower than most Augs on record, ranked against 68 other Augs held for this reservoir.

Storage, 1953–2026

Monthly mean storage
812 monthly values, 1953 to 2026
Monthly mean storageMonthly mean storage: Lake Granby in Mm³, from 1953.75 to 2026.5833333333333.0200400600800Mm³1953.751962.251970.751979.251992.752001.2520102018.5Year

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 812 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 812 would be longer than this page and unusable with a screen reader.
PeriodLake Granby (Mm³)
October 1953583
January 1954517
May 1954451
August 1954412
December 1954299
March 1955207
June 1955260
October 1955256
January 1956198
May 1956163
August 1956332
November 1956271
March 1957154
June 1957286
October 1957565
January 1958501
April 1958438
August 1958640
November 1958535
February 1959433
June 1959481
September 1959510
January 1960417
April 1960367
July 1960597
November 1960492
February 1961410
June 1961479
September 1961548
December 1961576
April 1962493
July 1962665
November 1962597
February 1963492
May 1963442
September 1963480
December 1963396
April 1964262
July 1964377
October 1964305
February 1965193
May 1965170
September 1965473
December 1965439
March 1966367
July 1966421
October 1966348
January 1967249
May 1967165
August 1967363
December 1967305
March 1968223
June 1968318
October 1968361
January 1969308
May 1969308
August 1969530
November 1969492
March 1970402
June 1970535
October 1970610
January 1971567
April 1971524
August 1971652
November 1971611
March 1972495
June 1972618
September 1972625
January 1973543
April 1973474
August 1973660
November 1973643
February 1974579
June 1974639
September 1974621
December 1974543
April 1975442
July 1975628
November 1975570
February 1976472
May 1976445
September 1976503
December 1976407
April 1977281
July 1977317
October 1977270
February 1978168
May 1978135
September 1978382
December 1978295
March 1979219
July 1979486
October 1979487
February 1980425
May 1980423
August 1980621
December 1985565
March 1986488
July 1986661
October 1986644
January 1987574
May 1987530
August 1987558
December 1987502
March 1988430
June 1988553
October 1988510
January 1989424
April 1989379
August 1989423
November 1989319
March 1990173
June 1990304
September 1990367
January 1991297
April 1991227
August 1991436
November 1991389
February 1992298
June 1992396
September 1992424
January 1993334
April 1993305
July 1993588
November 1993534
February 1994456
June 1994596
September 1994526
December 1994439
April 1995336
July 1995637
November 1995634
February 1996595
May 1996568
September 1996617
December 1996589
March 1997523
July 1997662
October 1997657
February 1998566
May 1998565
August 1998647
December 1998615
March 1999558
July 1999660
October 1999632
January 2000586
May 2000587
August 2000611
December 2000447
March 2001425
June 2001525
October 2001456
January 2002374
May 2002279
August 2002237
November 2002210
March 2003112
June 2003393
October 2003459
January 2004382
April 2004299
August 2004350
November 2004357
March 2005240
June 2005436
September 2005534
January 2006484
April 2006388
July 2006531
November 2006484
February 2007396
June 2007499
September 2007477
December 2007420
July 2008546
October 2008485
February 2009393
May 2009401
August 2009629
December 2009541
March 2010451
July 2010659
October 2010606
January 2011572
May 2011441
August 2011651
December 2011574
March 2012517
June 2012528
October 2012391
January 2013328
May 2013268
August 2013446
November 2013479
March 2014380
June 2014567
September 2014650
January 2015625
April 2015599
August 2015646
November 2015605
February 2016520
June 2016622
September 2016618
January 2017542
April 2017474
July 2017661
November 2017642
February 2018589
June 2018634
September 2018579
December 2018537
April 2019415
July 2019655
November 2019581
February 2020527
May 2020543
September 2020590
December 2020561
April 2021434
July 2021571
October 2021491
February 2022403
May 2022464
August 2022625
December 2022598
March 2023503
July 2023660
October 2023597
January 2024597
May 2024589
August 2024624
December 2024540
March 2025435
June 2025608
October 2025546
January 2026457
May 2026428
August 2026389

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 12.0200400600Mm³123456789101112Month1991–2020 average 1: 469 Mm³1991–2020 average 2: 442 Mm³1991–2020 average 3: 416 Mm³1991–2020 average 4: 401 Mm³1991–2020 average 5: 429 Mm³1991–2020 average 6: 527 Mm³1991–2020 average 7: 572 Mm³1991–2020 average 8: 562 Mm³1991–2020 average 9: 542 Mm³1991–2020 average 10: 530 Mm³1991–2020 average 11: 521 Mm³1991–2020 average 12: 502 Mm³Most recent 12 months 1: 457 Mm³Most recent 12 months 2: 420 Mm³Most recent 12 months 3: 400 Mm³Most recent 12 months 4: 423 Mm³Most recent 12 months 5: 428 Mm³Most recent 12 months 6: 454 Mm³Most recent 12 months 7: 432 Mm³Most recent 12 months 8: 389 Mm³Most recent 12 months 9: 568 Mm³Most recent 12 months 10: 546 Mm³Most recent 12 months 11: 533 Mm³Most recent 12 months 12: 497 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)
Jan469457
Feb442420
Mar416400
Apr401423
May429428
Jun527454
Jul572432
Aug562389
Sep542568
Oct530546
Nov521533
Dec502497

Why this page shows a volume and not a percentage

Water level

Monthly mean water surface elevation
812 monthly values
Monthly mean water surface elevationMonthly mean water surface elevation: Lake Granby in m, from 1953.75 to 2026.5833333333333.2,4252,4502,4752,5002,525m1953.751962.251970.751979.251992.752001.2520102018.5Year

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 812 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 812 would be longer than this page and unusable with a screen reader.
PeriodLake Granby (m)
1953.752,521
19542,518
1954.33333333333332,516
1954.58333333333332,514
1954.91666666666672,509
1955.16666666666672,504
1955.41666666666672,507
1955.752,507
19562,503
1956.33333333333332,501
1956.58333333333332,511
1956.83333333333332,507
1957.16666666666672,500
1957.41666666666672,508
1957.752,520
19582,518
1958.252,515
1958.58333333333332,523
1958.83333333333332,519
1959.08333333333332,515
1959.41666666666672,517
1959.66666666666672,518
19602,514
1960.252,512
1960.52,521
1960.83333333333332,517
1961.08333333333332,514
1961.41666666666672,517
1961.66666666666672,520
1961.91666666666672,521
1962.252,517
1962.52,524
1962.83333333333332,521
1963.08333333333332,517
1963.33333333333332,515
1963.66666666666672,517
1963.91666666666672,513
1964.252,507
1964.52,513
1964.752,509
1965.08333333333332,503
1965.33333333333332,501
1965.66666666666672,517
1965.91666666666672,515
1966.16666666666672,512
1966.52,514
1966.752,511
19672,506
1967.33333333333332,501
1967.58333333333332,512
1967.91666666666672,509
1968.16666666666672,505
1968.41666666666672,510
1968.752,512
19692,509
1969.33333333333332,509
1969.58333333333332,519
1969.83333333333332,517
1970.16666666666672,514
1970.41666666666672,519
1970.752,522
19712,520
1971.252,519
1971.58333333333332,523
1971.83333333333332,522
1972.16666666666672,518
1972.41666666666672,522
1972.66666666666672,522
19732,519
1973.252,517
1973.58333333333332,524
1973.83333333333332,523
1974.08333333333332,521
1974.41666666666672,523
1974.66666666666672,522
1974.91666666666672,519
1975.252,515
1975.52,522
1975.83333333333332,520
1976.08333333333332,517
1976.33333333333332,515
1976.66666666666672,518
1976.91666666666672,514
1977.252,508
1977.52,510
1977.752,507
1978.08333333333332,501
1978.33333333333332,499
1978.66666666666672,513
1978.91666666666672,509
1979.16666666666672,504
1979.52,517
1979.752,517
1980.08333333333332,515
1980.33333333333332,515
1980.58333333333332,522
1985.91666666666672,520
1986.16666666666672,517
1986.52,524
1986.752,523
19872,521
1987.33333333333332,519
1987.58333333333332,520
1987.91666666666672,518
1988.16666666666672,515
1988.41666666666672,520
1988.752,518
19892,515
1989.252,513
1989.58333333333332,515
1989.83333333333332,510
1990.16666666666672,502
1990.41666666666672,509
1990.66666666666672,512
19912,509
1991.252,505
1991.58333333333332,515
1991.83333333333332,513
1992.08333333333332,509
1992.41666666666672,513
1992.66666666666672,515
19932,511
1993.252,509
1993.52,521
1993.83333333333332,519
1994.08333333333332,516
1994.41666666666672,521
1994.66666666666672,519
1994.91666666666672,515
1995.252,511
1995.52,523
1995.83333333333332,523
1996.08333333333332,521
1996.33333333333332,520
1996.66666666666672,522
1996.91666666666672,521
1997.16666666666672,519
1997.52,524
1997.752,523
1998.08333333333332,520
1998.33333333333332,520
1998.58333333333332,523
1998.91666666666672,522
1999.16666666666672,520
1999.52,524
1999.752,523
20002,521
2000.33333333333332,520
2000.58333333333332,522
2000.91666666666672,515
2001.16666666666672,515
2001.41666666666672,519
2001.752,516
20022,512
2002.33333333333332,508
2002.58333333333332,506
2002.83333333333332,504
2003.16666666666672,497
2003.41666666666672,513
2003.752,516
20042,513
2004.252,509
2004.58333333333332,511
2004.83333333333332,512
2005.16666666666672,506
2005.41666666666672,515
2005.66666666666672,519
20062,517
2006.252,513
2006.52,519
2006.83333333333332,517
2007.08333333333332,513
2007.41666666666672,518
2007.66666666666672,517
2007.91666666666672,514
2008.52,519
2008.752,517
2009.08333333333332,513
2009.33333333333332,514
2009.58333333333332,522
2009.91666666666672,519
2010.16666666666672,516
2010.52,524
2010.752,522
20112,520
2011.33333333333332,515
2011.58333333333332,523
2011.91666666666672,521
2012.16666666666672,518
2012.41666666666672,519
2012.752,513
20132,510
2013.33333333333332,507
2013.58333333333332,516
2013.83333333333332,517
2014.16666666666672,513
2014.41666666666672,520
2014.66666666666672,523
20152,522
2015.252,521
2015.58333333333332,523
2015.83333333333332,522
2016.08333333333332,518
2016.41666666666672,522
2016.66666666666672,522
20172,519
2017.252,517
2017.52,524
2017.83333333333332,523
2018.08333333333332,521
2018.41666666666672,523
2018.66666666666672,521
2018.91666666666672,519
2019.252,514
2019.52,523
2019.83333333333332,521
2020.08333333333332,519
2020.33333333333332,519
2020.66666666666672,521
2020.91666666666672,520
2021.252,515
2021.52,439
2021.752,517
2022.08333333333332,514
2022.33333333333332,516
2022.58333333333332,522
2022.91666666666672,521
2023.16666666666672,518
2023.52,524
2023.752,521
20242,521
2024.33333333333332,521
2024.58333333333332,522
2024.91666666666672,519
2025.16666666666672,515
2025.41666666666672,522
2025.752,519
20262,516
2026.33333333333332,515
2026.58333333333332,513

Rate and persistence

-18.35 Mm³
Mean drawdown per month over 12 months
2 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

Lake Granby
Gauge location
Lake GranbyLake Granby — 389.40 Mm³Lake Granby — 389.40 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 held1953–2026
Completeness91.4% 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.
Continuity91% of the months between 1953 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), Lake Granby reservoir records, accessed 2026-09-02, hydrionis.com/reservoirs/reservoir-usbr-351/

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 Lake Granby 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

812 monthly observations 1953–2026 Mm³
Spatially aggregatedHigh confidenceAugust 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 383. 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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