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

346.37 Mm³
Stored, September 2026
10th
Percentile among 68 Seps on record
-36.1%
Against the Sep 1991–2020 average
-39.0%
Change over the 12 months to 2026-09

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

Storage, 1953–2026

Monthly mean storage
813 monthly values, 1953 to 2026
Monthly mean storageMonthly mean storage: Lake Granby in Mm³, from 1953.75 to 2026.6666666666667.0200400600800Mm³1953.751962.251970.751979.251992.752001.2520102018.5Year

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 813 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 813 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
March 1959409
June 1959481
September 1959510
January 1960417
April 1960367
August 1960584
November 1960492
February 1961410
June 1961479
September 1961548
January 1962559
April 1962493
July 1962665
November 1962597
February 1963492
June 1963491
September 1963480
December 1963396
April 1964262
July 1964377
November 1964278
February 1965193
May 1965170
September 1965473
December 1965439
March 1966367
July 1966421
October 1966348
February 1967218
May 1967165
August 1967363
December 1967305
March 1968223
July 1968394
October 1968361
January 1969308
May 1969308
August 1969530
December 1969475
March 1970402
June 1970535
October 1970610
January 1971567
May 1971527
August 1971652
November 1971611
March 1972495
June 1972618
October 1972614
January 1973543
April 1973474
August 1973660
November 1973643
March 1974559
June 1974639
September 1974621
January 1975514
April 1975442
August 1975642
November 1975570
February 1976472
June 1976514
September 1976503
January 1977375
April 1977281
July 1977317
November 1977253
February 1978168
June 1978266
September 1978382
December 1978295
April 1979204
July 1979486
November 1979473
February 1980425
May 1980423
September 1980604
December 1985565
April 1986465
July 1986661
October 1986644
February 1987548
May 1987530
September 1987522
December 1987502
March 1988430
July 1988602
October 1988510
February 1989399
May 1989401
August 1989423
December 1989280
March 1990173
July 1990369
October 1990357
January 1991297
May 1991236
August 1991436
December 1991358
March 1992278
June 1992396
October 1992416
January 1993334
April 1993305
August 1993584
November 1993534
March 1994437
June 1994596
September 1994526
January 1995404
April 1995336
August 1995659
November 1995634
February 1996595
June 1996647
September 1996617
January 1997568
April 1997522
July 1997662
November 1997647
February 1998566
June 1998641
September 1998619
December 1998615
April 1999529
July 1999660
November 1999625
February 2000564
May 2000587
September 2000578
December 2000447
April 2001425
July 2001518
October 2001456
February 2002340
May 2002279
September 2002220
December 2002180
March 2003112
July 2003491
October 2003459
February 2004348
May 2004304
August 2004350
December 2004334
March 2005240
July 2005528
October 2005522
January 2006484
May 2006425
August 2006498
December 2006465
March 2007368
June 2007499
October 2007463
April 2008333
August 2008542
November 2008470
February 2009393
June 2009546
September 2009604
January 2010512
April 2010425
July 2010659
November 2010606
February 2011539
June 2011513
September 2011631
December 2011574
April 2012512
July 2012502
November 2012373
February 2013291
May 2013268
September 2013449
December 2013479
April 2014356
July 2014655
October 2014649
February 2015603
May 2015615
August 2015646
December 2015594
March 2016482
July 2016658
October 2016592
January 2017542
May 2017514
August 2017660
December 2017638
March 2018551
June 2018634
October 2018560
January 2019501
May 2019441
August 2019648
November 2019581
March 2020502
June 2020637
October 2020583
January 2021523
April 2021434
August 2021546
November 2021478
March 2022376
June 2022597
September 2022597
January 2023576
April 2023478
August 2023644
November 2023596
February 2024602
June 2024646
September 2024592
January 2025502
April 2025439
July 2025645
November 2025533
February 2026420
June 2026454
September 2026346

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: 346 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
Sep542346
Oct530546
Nov521533
Dec502497

Why this page shows a volume and not a percentage

Water level

Monthly mean water surface elevation
813 monthly values
Monthly mean water surface elevationMonthly mean water surface elevation: Lake Granby in m, from 1953.75 to 2026.6666666666667.2,4252,4502,4752,5002,525m1953.751962.251970.751979.251992.752001.2520102018.5Year

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 813 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 813 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
1959.16666666666672,514
1959.41666666666672,517
1959.66666666666672,518
19602,514
1960.252,512
1960.58333333333332,521
1960.83333333333332,517
1961.08333333333332,514
1961.41666666666672,517
1961.66666666666672,520
19622,520
1962.252,517
1962.52,524
1962.83333333333332,521
1963.08333333333332,517
1963.41666666666672,517
1963.66666666666672,517
1963.91666666666672,513
1964.252,507
1964.52,513
1964.83333333333332,508
1965.08333333333332,503
1965.33333333333332,501
1965.66666666666672,517
1965.91666666666672,515
1966.16666666666672,512
1966.52,514
1966.752,511
1967.08333333333332,504
1967.33333333333332,501
1967.58333333333332,512
1967.91666666666672,509
1968.16666666666672,505
1968.52,513
1968.752,512
19692,509
1969.33333333333332,509
1969.58333333333332,519
1969.91666666666672,517
1970.16666666666672,514
1970.41666666666672,519
1970.752,522
19712,520
1971.33333333333332,519
1971.58333333333332,523
1971.83333333333332,522
1972.16666666666672,518
1972.41666666666672,522
1972.752,522
19732,519
1973.252,517
1973.58333333333332,524
1973.83333333333332,523
1974.16666666666672,520
1974.41666666666672,523
1974.66666666666672,522
19752,518
1975.252,515
1975.58333333333332,523
1975.83333333333332,520
1976.08333333333332,517
1976.41666666666672,518
1976.66666666666672,518
19772,512
1977.252,508
1977.52,510
1977.83333333333332,506
1978.08333333333332,501
1978.41666666666672,507
1978.66666666666672,513
1978.91666666666672,509
1979.252,504
1979.52,517
1979.83333333333332,517
1980.08333333333332,515
1980.33333333333332,515
1980.66666666666672,522
1985.91666666666672,520
1986.252,516
1986.52,524
1986.752,523
1987.08333333333332,520
1987.33333333333332,519
1987.66666666666672,518
1987.91666666666672,518
1988.16666666666672,515
1988.52,522
1988.752,518
1989.08333333333332,514
1989.33333333333332,514
1989.58333333333332,515
1989.91666666666672,508
1990.16666666666672,502
1990.52,512
1990.752,512
19912,509
1991.33333333333332,505
1991.58333333333332,515
1991.91666666666672,512
1992.16666666666672,508
1992.41666666666672,513
1992.752,514
19932,511
1993.252,509
1993.58333333333332,521
1993.83333333333332,519
1994.16666666666672,515
1994.41666666666672,521
1994.66666666666672,519
19952,514
1995.252,511
1995.58333333333332,524
1995.83333333333332,523
1996.08333333333332,521
1996.41666666666672,523
1996.66666666666672,522
19972,520
1997.252,519
1997.52,524
1997.83333333333332,523
1998.08333333333332,520
1998.41666666666672,523
1998.66666666666672,522
1998.91666666666672,522
1999.252,519
1999.52,524
1999.83333333333332,522
2000.08333333333332,520
2000.33333333333332,520
2000.66666666666672,521
2000.91666666666672,515
2001.252,515
2001.52,518
2001.752,516
2002.08333333333332,511
2002.33333333333332,508
2002.66666666666672,505
2002.91666666666672,502
2003.16666666666672,497
2003.52,517
2003.752,516
2004.08333333333332,511
2004.33333333333332,509
2004.58333333333332,511
2004.91666666666672,511
2005.16666666666672,506
2005.52,519
2005.752,519
20062,517
2006.33333333333332,515
2006.58333333333332,518
2006.91666666666672,516
2007.16666666666672,512
2007.41666666666672,518
2007.752,516
2008.252,511
2008.58333333333332,519
2008.83333333333332,517
2009.08333333333332,513
2009.41666666666672,519
2009.66666666666672,522
20102,518
2010.252,515
2010.52,524
2010.83333333333332,522
2011.08333333333332,519
2011.41666666666672,518
2011.66666666666672,523
2011.91666666666672,521
2012.252,518
2012.52,518
2012.83333333333332,512
2013.08333333333332,508
2013.33333333333332,507
2013.66666666666672,516
2013.91666666666672,517
2014.252,512
2014.52,523
2014.752,523
2015.08333333333332,522
2015.33333333333332,522
2015.58333333333332,523
2015.91666666666672,521
2016.16666666666672,517
2016.52,523
2016.752,521
20172,519
2017.33333333333332,518
2017.58333333333332,524
2017.91666666666672,523
2018.16666666666672,520
2018.41666666666672,523
2018.752,520
20192,518
2019.33333333333332,515
2019.58333333333332,523
2019.83333333333332,521
2020.16666666666672,518
2020.41666666666672,523
2020.752,521
20212,519
2021.252,515
2021.58333333333332,519
2021.83333333333332,517
2022.16666666666672,513
2022.41666666666672,521
2022.66666666666672,521
20232,521
2023.252,517
2023.58333333333332,523
2023.83333333333332,521
2024.08333333333332,522
2024.41666666666672,523
2024.66666666666672,521
20252,518
2025.252,515
2025.52,523
2025.83333333333332,519
2026.08333333333332,514
2026.41666666666672,516
2026.66666666666672,511

Rate and persistence

-18.49 Mm³
Mean drawdown per month over 12 months
3 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 — 346.37 Mm³Lake Granby — 346.37 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
Completeness91.6% 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.
Continuity92% of the months between 1953 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), Lake Granby reservoir records, accessed 2026-10-05, 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

813 monthly observations 1953–2026 Mm³
Spatially aggregatedHigh confidenceSeptember 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 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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