HydrionisGlobal Water Intelligence
Monitored reservoir

Seminoe Reservoir

Seminoe Reservoir is a federal reservoir operated by the United States Bureau of Reclamation in its Great Plains region, with published operating records from 1945.

Storage recordSeminoe Reservoir Dam and Powerplant

Storage now, against this reservoir's own record

351.26 Mm³
Stored, August 2026
1st
Percentile among 81 Augs on record
-57.7%
Against the Aug 1991–2020 average
-31.1%
Change over the 12 months to 2026-08

Storage in August 2026 was lower than almost every other Aug on record, ranked against 81 other Augs held for this reservoir.

Storage, 1945–2026

Monthly mean storage
971 monthly values, 1945 to 2026
Monthly mean storageMonthly mean storage: Seminoe Reservoir in Mm³, from 1945.75 to 2026.5833333333333.05001,0001,500Mm³1945.751955.91666666666671966.08333333333331976.251986.41666666666671996.58333333333332006.752016.9166666666667Year

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 971 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 971 would be longer than this page and unusable with a screen reader.
PeriodSeminoe Reservoir (Mm³)
October 1945891
February 1946704
June 1946943
October 1946652
February 1947443
June 1947971
October 19471,039
February 1948804
June 19481,135
November 1948806
March 1949654
July 19491,263
November 1949975
March 1950725
July 19501,097
November 1950851
March 1951662
July 19511,250
November 19511,084
March 1952725
July 19521,277
November 1952962
March 1953740
July 1953922
November 1953526
March 1954297
August 1954439
December 1954419
April 1955403
August 1955563
December 1955434
April 1956344
August 1956595
December 1956364
April 1957312
August 19571,263
December 1957890
April 1958682
August 19581,167
December 19581,111
April 1959700
August 1959746
December 1959555
May 1960378
September 1960436
January 1961149
May 1961101
September 1961313
January 1962228
May 1962536
September 1962939
January 1963442
May 1963528
September 1963633
January 1964396
May 1964167
September 1964446
January 1965276
May 1965166
September 1965852
February 1966538
June 1966642
October 1966386
February 1967192
June 1967343
October 1967583
February 1968325
June 1968733
October 1968955
February 1969554
June 1969833
October 1969775
February 1970439
June 1970872
October 19701,009
February 1971580
June 1971924
November 19711,022
March 1972751
July 19721,166
November 1972984
March 1973611
July 19731,215
November 19731,086
March 1974756
July 19741,192
November 1974942
March 1975571
July 19751,165
November 1975965
March 1976679
July 19761,093
November 1976881
March 1977602
August 1977791
December 1977571
April 1978310
August 19781,056
December 1978797
April 1979425
August 19791,106
December 1979828
April 1980425
August 19801,152
December 1980913
April 1981591
August 1981725
December 1981528
April 1982244
August 19821,075
December 1982940
May 1983749
September 19831,145
January 19841,010
May 1984946
September 19841,159
January 19851,065
May 19851,101
September 19851,014
January 1986820
May 1986685
September 19861,005
January 1987869
May 1987965
September 1987835
January 1988631
May 1988727
September 1988976
January 1989694
June 1989661
October 1989589
February 1990471
June 1990545
October 1990523
February 1991433
June 1991718
October 1991530
February 1992473
June 1992554
October 1992328
February 1993276
June 1993839
October 1993753
February 1994692
June 1994852
October 1994418
March 1995372
July 19951,179
November 19951,015
March 1996863
July 19961,114
November 1996971
March 1997793
July 19971,151
November 19971,111
March 1998981
July 19981,175
November 19981,028
March 1999838
July 19991,186
November 19991,082
March 2000949
July 20001,183
December 2000907
April 2001810
August 2001840
December 2001650
April 2002530
August 2002425
December 2002302
April 2003278
August 2003453
December 2003364
April 2004380
August 2004379
December 2004336
April 2005378
August 2005629
December 2005513
April 2006511
September 2006335
January 2007336
May 2007460
September 2007289
January 2008248
May 2008346
September 2008669
January 2009628
May 2009739
September 2009886
January 2010843
May 2010915
September 20101,069
January 20111,046
May 2011518
September 20111,087
January 20121,082
June 2012971
October 2012682
February 2013606
June 2013715
October 2013403
February 2014388
June 2014950
October 2014860
February 2015879
June 20151,069
October 2015987
February 2016865
June 20161,118
October 2016973
February 2017937
June 20171,089
October 20171,004
March 2018990
July 2018935
November 2018802
March 2019752
July 20191,119
November 2019992
March 2020949
July 2020986
November 2020779
March 2021704
July 2021528
November 2021386
March 2022346
July 2022672
November 2022583
March 2023537
July 20231,035
December 2023807
April 2024801
August 2024768
December 2024629
April 2025614
August 2025510
December 2025427
April 2026411
August 2026351

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 12.02505007501,000Mm³123456789101112Month1991–2020 average 1: 694 Mm³1991–2020 average 2: 677 Mm³1991–2020 average 3: 660 Mm³1991–2020 average 4: 658 Mm³1991–2020 average 5: 703 Mm³1991–2020 average 6: 873 Mm³1991–2020 average 7: 900 Mm³1991–2020 average 8: 831 Mm³1991–2020 average 9: 772 Mm³1991–2020 average 10: 747 Mm³1991–2020 average 11: 736 Mm³1991–2020 average 12: 720 Mm³Most recent 12 months 1: 416 Mm³Most recent 12 months 2: 402 Mm³Most recent 12 months 3: 397 Mm³Most recent 12 months 4: 411 Mm³Most recent 12 months 5: 436 Mm³Most recent 12 months 6: 472 Mm³Most recent 12 months 7: 430 Mm³Most recent 12 months 8: 351 Mm³Most recent 12 months 9: 478 Mm³Most recent 12 months 10: 458 Mm³Most recent 12 months 11: 443 Mm³Most recent 12 months 12: 427 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)
Jan694416
Feb677402
Mar660397
Apr658411
May703436
Jun873472
Jul900430
Aug831351
Sep772478
Oct747458
Nov736443
Dec720427

Why this page shows a volume and not a percentage

Water level

Monthly mean water surface elevation
971 monthly values
Monthly mean water surface elevationMonthly mean water surface elevation: Seminoe Reservoir in m, from 1945.75 to 2026.5833333333333.1,9001,9101,9201,9301,940m1945.751955.91666666666671966.08333333333331976.251986.41666666666671996.58333333333332006.752016.9166666666667Year

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 971 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 971 would be longer than this page and unusable with a screen reader.
PeriodSeminoe Reservoir (m)
1945.751,932
1946.08333333333331,929
1946.41666666666671,933
1946.751,928
1947.08333333333331,923
1947.41666666666671,934
1947.751,935
1948.08333333333331,931
1948.41666666666671,936
1948.83333333333331,931
1949.16666666666671,928
1949.51,938
1949.83333333333331,934
1950.16666666666671,929
1950.51,935
1950.83333333333331,932
1951.16666666666671,928
1951.51,937
1951.83333333333331,935
1952.16666666666671,929
1952.51,938
1952.83333333333331,933
1953.16666666666671,930
1953.51,933
1953.83333333333331,926
1954.16666666666671,919
1954.58333333333331,923
1954.91666666666671,923
1955.251,922
1955.58333333333331,926
1955.91666666666671,923
1956.251,920
1956.58333333333331,927
1956.91666666666671,921
1957.251,919
1957.58333333333331,938
1957.91666666666671,933
1958.251,929
1958.58333333333331,937
1958.91666666666671,936
1959.251,929
1959.58333333333331,930
1959.91666666666671,926
1960.33333333333331,922
1960.66666666666671,923
19611,912
1961.33333333333331,909
1961.66666666666671,919
19621,916
1962.33333333333331,926
1962.66666666666671,933
19631,923
1963.33333333333331,926
1963.66666666666671,928
19641,922
1964.33333333333331,913
1964.66666666666671,924
19651,918
1965.33333333333331,913
1965.66666666666671,932
1966.08333333333331,926
1966.41666666666671,928
1966.751,922
1967.08333333333331,914
1967.41666666666671,920
1967.751,927
1968.08333333333331,920
1968.41666666666671,930
1968.751,934
1969.08333333333331,926
1969.41666666666671,932
1969.751,931
1970.08333333333331,923
1970.41666666666671,932
1970.751,934
1971.08333333333331,927
1971.41666666666671,933
1971.83333333333331,935
1972.16666666666671,930
1972.51,937
1972.83333333333331,934
1973.16666666666671,927
1973.51,937
1973.83333333333331,936
1974.16666666666671,930
1974.51,937
1974.83333333333331,933
1975.16666666666671,927
1975.51,937
1975.83333333333331,934
1976.16666666666671,929
1976.51,936
1976.83333333333331,932
1977.16666666666671,927
1977.58333333333331,931
1977.91666666666671,926
1978.251,919
1978.58333333333331,935
1978.91666666666671,931
1979.251,923
1979.58333333333331,936
1979.91666666666671,932
1980.251,923
1980.58333333333331,936
1980.91666666666671,933
1981.251,927
1981.58333333333331,930
1981.91666666666671,925
1982.251,917
1982.58333333333331,935
1982.91666666666671,933
1983.33333333333331,930
1983.66666666666671,936
19841,934
1984.33333333333331,933
1984.66666666666671,936
19851,935
1985.33333333333331,936
1985.66666666666671,934
19861,931
1986.33333333333331,929
1986.66666666666671,934
19871,932
1987.33333333333331,934
1987.66666666666671,932
19881,928
1988.33333333333331,930
1988.66666666666671,934
19891,929
1989.41666666666671,928
1989.751,927
1990.08333333333331,924
1990.41666666666671,926
1990.751,925
1991.08333333333331,923
1991.41666666666671,929
1991.751,926
1992.08333333333331,924
1992.41666666666671,926
1992.751,920
1993.08333333333331,918
1993.41666666666671,932
1993.751,930
1994.08333333333331,929
1994.41666666666671,932
1994.751,923
1995.16666666666671,921
1995.51,937
1995.83333333333331,934
1996.16666666666671,932
1996.51,936
1996.83333333333331,934
1997.16666666666671,931
1997.51,936
1997.83333333333331,936
1998.16666666666671,934
1998.51,937
1998.83333333333331,935
1999.16666666666671,932
1999.51,937
1999.83333333333331,935
2000.16666666666671,933
2000.51,937
2000.91666666666671,933
2001.251,931
2001.58333333333331,932
2001.91666666666671,928
2002.251,926
2002.58333333333331,923
2002.91666666666671,919
2003.251,918
2003.58333333333331,924
2003.91666666666671,921
2004.251,921
2004.58333333333331,921
2004.91666666666671,920
2005.251,921
2005.58333333333331,928
2005.91666666666671,925
2006.251,925
2006.66666666666671,920
20071,920
2007.33333333333331,924
2007.66666666666671,918
20081,917
2008.33333333333331,920
2008.66666666666671,929
20091,928
2009.33333333333331,930
2009.66666666666671,932
20101,932
2010.33333333333331,933
2010.66666666666671,935
20111,935
2011.33333333333331,925
2011.66666666666671,935
20121,935
2012.41666666666671,934
2012.751,929
2013.08333333333331,927
2013.41666666666671,929
2013.751,922
2014.08333333333331,922
2014.41666666666671,933
2014.751,932
2015.08333333333331,932
2015.41666666666671,935
2015.751,934
2016.08333333333331,932
2016.41666666666671,936
2016.751,934
2017.08333333333331,933
2017.41666666666671,935
2017.751,934
2018.16666666666671,934
2018.51,933
2018.83333333333331,931
2019.16666666666671,930
2019.51,936
2019.83333333333331,934
2020.16666666666671,933
2020.51,934
2020.83333333333331,931
2021.16666666666671,929
2021.51,925
2021.83333333333331,922
2022.16666666666671,920
2022.51,929
2022.83333333333331,927
2023.16666666666671,926
2023.51,935
2023.91666666666671,931
2024.251,931
2024.58333333333331,930
2024.91666666666671,928
2025.251,927
2025.58333333333331,925
2025.91666666666671,923
2026.251,922
2026.58333333333331,921

Rate and persistence

-13.24 Mm³
Mean drawdown per month over 12 months
11 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

Seminoe Reservoir
Gauge location
Seminoe ReservoirSeminoe Reservoir — 351.26 Mm³Seminoe Reservoir — 351.26 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 held1945–2026
Completeness98.7% 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.
Continuity99% of the months between 1945 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), Seminoe Reservoir reservoir records, accessed 2026-09-02, hydrionis.com/reservoirs/reservoir-usbr-467/

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 Seminoe 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

971 monthly observations 1945–2026 Mm³
Spatially aggregatedHigh confidenceAugust 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 732. 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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