Hyatt Reservoir — storage

Storage now, against this reservoir's own record

6.69 Mm³

Stored, September 2026

24th

Percentile among 60 Seps on record

-33.5%

Against the Sep 1991–2020 average

-54.5%

Change over the 12 months to 2026-09

Storage in September 2026 was lower than most Seps on record, ranked against 60 other Seps held for this reservoir.

Storage, 1966–2026

Monthly mean storage

719 monthly values, 1966 to 2026

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 719 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 719 would be longer than this page and unusable with a screen reader.
Period	Hyatt Reservoir (Mm³)
October 1966	11.0
January 1967	12.5
April 1967	16.4
July 1967	17.9
October 1967	10.3
January 1968	10.9
April 1968	13.9
July 1968	11.5
October 1968	8.72
January 1969	9.79
April 1969	13.6
July 1969	17.6
October 1969	13.5
January 1970	15.2
April 1970	19.9
July 1970	17.4
October 1970	12.8
January 1971	15.5
April 1971	19.8
July 1971	18.8
October 1971	15.2
January 1972	18.0
April 1972	19.2
July 1972	17.1
October 1972	9.47
January 1973	11.0
April 1973	13.9
July 1973	12.8
October 1973	9.51
January 1974	15.3
April 1974	19.7
July 1974	16.3
October 1974	11.4
January 1975	13.2
April 1975	16.8
July 1975	17.9
October 1975	13.0
January 1976	15.4
April 1976	19.0
July 1976	16.7
October 1976	12.4
January 1977	12.4
April 1977	13.3
July 1977	11.0
October 1977	6.86
January 1978	10.9
April 1978	16.6
July 1978	15.2
October 1978	10.8
January 1979	12.6
April 1979	17.5
July 1979	17.5
October 1979	12.5
January 1980	15.0
April 1980	19.7
July 1980	18.3
October 1980	12.2
January 1981	13.1
April 1981	15.2
July 1981	13.3
October 1981	9.66
January 1982	15.0
April 1982	19.9
July 1982	18.2
October 1982	13.4
January 1983	15.4
April 1983	20.0
July 1983	18.4
October 1983	13.5
January 1984	17.3
April 1984	19.8
July 1984	17.9
October 1984	13.1
January 1985	15.9
April 1985	19.2
July 1985	15.7
October 1985	11.6
January 1986	12.8
April 1986	19.9
July 1986	17.1
October 1986	12.0
January 1987	12.7
April 1987	15.3
July 1987	10.5
October 1987	6.31
January 1988	7.39
April 1988	9.74
July 1988	6.54
October 1988	2.27
January 1989	3.62
April 1989	10.1
July 1989	11.9
October 1989	3.74
January 1990	4.52
April 1990	7.86
July 1990	7.64
October 1990	3.63
January 1991	4.48
April 1991	7.44
July 1991	9.66
October 1991	5.57
February 1992	6.91
May 1992	7.43
August 1992	3.60
November 1992	3.57
February 1993	3.57
May 1993	12.4
August 1993	13.1
November 1993	12.2
February 1994	12.9
May 1994	13.1
August 1994	3.74
November 1994	3.29
February 1995	4.28
May 1995	14.4
August 1995	13.6
November 1995	11.3
February 1996	18.5
May 1996	20.3
August 1996	14.5
December 1996	15.6
March 1997	20.0
June 1997	16.5
September 1997	11.7
December 1997	11.7
March 1998	16.1
June 1998	20.0
September 1998	14.1
December 1998	14.4
March 1999	15.0
June 1999	19.4
September 1999	13.8
December 1999	13.3
March 2000	15.8
June 2000	18.5
September 2000	12.0
December 2000	12.0
March 2001	13.1
June 2001	11.5
September 2001	3.27
December 2001	3.56
March 2002	6.27
June 2002	11.3
September 2002	6.94
December 2002	7.16
March 2003	10.6
June 2003	16.0
September 2003	11.4
December 2003	11.9
March 2004	15.6
June 2004	19.3
September 2004	13.9
December 2004	14.6
March 2005	16.3
June 2005	19.9
September 2005	16.7
December 2005	18.2
March 2006	19.9
June 2006	19.7
September 2006	16.5
December 2006	17.0
March 2007	20.0
June 2007	19.3
September 2007	15.3
December 2007	15.9
March 2008	18.2
June 2008	19.4
September 2008	16.3
December 2008	16.5
March 2009	18.6
June 2009	18.7
September 2009	14.5
December 2009	14.7
March 2010	15.2
June 2010	17.8
September 2010	14.2
December 2010	14.5
March 2011	18.2
June 2011	19.6
September 2011	16.8
December 2011	16.3
March 2012	18.1
June 2012	18.7
September 2012	14.1
December 2012	14.5
March 2013	16.8
June 2013	16.9
September 2013	11.4
December 2013	11.5
March 2014	10.8
June 2014	7.43
September 2014	1.40
December 2014	2.35
March 2015	7.65
June 2015	7.29
September 2015	1.48
December 2015	2.00
March 2016	9.73
June 2016	13.8
September 2016	8.50
December 2016	9.61
March 2017	12.4
June 2017	12.0
September 2017	8.00
December 2017	8.47
March 2018	8.05
June 2018	7.31
September 2018	1.13
December 2018	1.17
March 2019	3.66
June 2019	10.7
September 2019	7.07
December 2019	7.40
March 2020	9.44
June 2020	7.58
September 2020	1.19
December 2020	1.08
March 2021	2.53
June 2021	3.43
September 2021	0.255
December 2021	0.607
March 2022	2.02
June 2022	1.54
September 2022	0.385
December 2022	0.826
March 2023	3.34
June 2023	11.6
September 2023	8.04
December 2023	8.40
March 2024	10.3
June 2024	11.7
September 2024	7.50
December 2024	8.05
March 2025	12.9
June 2025	18.4
September 2025	14.7
December 2025	14.8
March 2026	14.8
June 2026	9.55
September 2026	6.69

The reservoir's year

Seasonal storage profile

Each calendar month's reference average, against the most recent year

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
Period	1991–2020 average (Mm³)	Most recent 12 months (Mm³)
Jan	11.5	15.7
Feb	12.3	15.5
Mar	13.1	14.8
Apr	14.7	12.2
May	15.5	10.3
Jun	14.9	9.55
Jul	13.3	8.56
Aug	11.4	7.37
Sep	10.1	6.69
Oct	9.67	14.3
Nov	10.0	14.5
Dec	10.5	14.8

Why this page shows a volume and not a percentage

Percentage full is a division, and the denominator is missing

“Percentage full” is the figure a drought is discussed in, and it is stored volume divided by capacity. Capacity is published on several different bases — gross, usable, live, and the figure at a particular spillway or licence condition — and dividing a stored volume by the wrong one produces a percentage confidently wrong by the ratio between them, at exactly the moment the number matters most.

Hydrionis holds storage measurements for this reservoir and does not hold a compatible authoritative capacity figure for it, so percentage full is not calculated. The volume above is what was actually measured. Where you need a percentage, take the publisher’s own capacity on its own stated basis and divide it yourself — the source is linked below, and knowing which basis you used is the whole point.

Water level

Monthly mean water surface elevation

667 monthly values

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 667 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 667 would be longer than this page and unusable with a screen reader.
Period	Hyatt Reservoir (m)
1967.9166666666667	1,526
1968.1666666666667	1,527
1968.4166666666667	1,527
1968.5833333333333	1,526
1968.8333333333333	1,525
1969.0833333333333	1,526
1969.3333333333333	1,529
1969.5833333333333	1,528
1969.75	1,527
1970	1,527
1970.25	1,529
1970.5	1,528
1970.6666666666667	1,527
1970.9166666666667	1,527
1971.1666666666667	1,529
1971.4166666666667	1,529
1971.6666666666667	1,528
1971.8333333333333	1,528
1972.0833333333333	1,529
1972.3333333333333	1,529
1972.5833333333333	1,527
1972.8333333333333	1,526
1973	1,526
1973.25	1,527
1973.5	1,527
1973.75	1,526
1973.9166666666667	1,527
1974.1666666666667	1,528
1974.4166666666667	1,529
1974.6666666666667	1,527
1974.9166666666667	1,526
1975.0833333333333	1,527
1975.3333333333333	1,529
1975.5833333333333	1,528
1975.8333333333333	1,527
1976.0833333333333	1,528
1976.25	1,529
1976.5	1,528
1976.75	1,527
1977	1,527
1977.1666666666667	1,527
1977.4166666666667	1,527
1977.6666666666667	1,525
1977.9166666666667	1,525
1978.1666666666667	1,527
1978.3333333333333	1,528
1978.5833333333333	1,527
1978.8333333333333	1,526
1979.0833333333333	1,527
1979.3333333333333	1,529
1979.5	1,528
1979.75	1,527
1980	1,527
1980.25	1,529
1980.4166666666667	1,529
1980.6666666666667	1,527
1980.9166666666667	1,527
1981.1666666666667	1,527
1981.4166666666667	1,527
1981.5833333333333	1,526
1981.8333333333333	1,526
1982.0833333333333	1,528
1982.3333333333333	1,529
1982.5833333333333	1,528
1982.75	1,527
1983	1,528
1983.25	1,529
1983.5	1,528
1983.6666666666667	1,527
1983.9166666666667	1,527
1984.1666666666667	1,529
1984.4166666666667	1,529
1984.6666666666667	1,527
1984.8333333333333	1,527
1985.0833333333333	1,528
1985.3333333333333	1,529
1985.5833333333333	1,527
1985.8333333333333	1,526
1986	1,527
1986.25	1,529
1986.5	1,528
1986.75	1,526
1987	1,527
1987.1666666666667	1,527
1987.4166666666667	1,527
1987.6666666666667	1,524
1987.9166666666667	1,524
1988.0833333333333	1,525
1988.3333333333333	1,525
1988.5833333333333	1,523
1992.0833333333333	1,524
1992.3333333333333	1,525
1992.5	1,523
1992.75	1,523
1993	1,523
1993.25	1,525
1993.5	1,527
1993.6666666666667	1,527
1993.9166666666667	1,527
1994.1666666666667	1,527
1994.4166666666667	1,526
1994.5833333333333	1,523
1994.8333333333333	1,523
1995.0833333333333	1,523
1995.3333333333333	1,527
1995.5833333333333	1,527
1995.75	1,526
1996	1,528
1996.25	1,529
1996.5	1,528
1996.75	1,526
1996.9166666666667	1,528
1997.1666666666667	1,529
1997.4166666666667	1,528
1997.6666666666667	1,526
1997.8333333333333	1,526
1998.0833333333333	1,527
1998.3333333333333	1,529
1998.5833333333333	1,528
1998.8333333333333	1,527
1999	1,527
1999.25	1,528
1999.5	1,528
1999.75	1,527
2000	1,527
2000.1666666666667	1,528
2000.4166666666667	1,528
2000.6666666666667	1,526
2000.9166666666667	1,526
2001.0833333333333	1,527
2001.3333333333333	1,527
2001.5833333333333	1,524
2001.8333333333333	1,523
2002.0833333333333	1,524
2002.25	1,526
2002.5	1,526
2002.75	1,524
2003	1,525
2003.25	1,527
2003.4166666666667	1,528
2003.6666666666667	1,526
2003.9166666666667	1,526
2004.1666666666667	1,528
2004.3333333333333	1,529
2004.5833333333333	1,527
2004.8333333333333	1,527
2005.0833333333333	1,528
2005.3333333333333	1,529
2005.5	1,529
2005.75	1,528
2006	1,529
2006.25	1,529
2006.5	1,529
2006.6666666666667	1,528
2006.9166666666667	1,528
2007.1666666666667	1,529
2007.4166666666667	1,529
2007.5833333333333	1,528
2007.8333333333333	1,528
2008.0833333333333	1,528
2008.3333333333333	1,529
2008.5833333333333	1,528
2008.75	1,528
2009	1,528
2009.25	1,529
2009.5	1,528
2009.75	1,527
2009.9166666666667	1,527
2010.1666666666667	1,527
2010.4166666666667	1,528
2010.6666666666667	1,527
2010.9166666666667	1,527
2011.0833333333333	1,528
2011.3333333333333	1,529
2011.5833333333333	1,528
2011.8333333333333	1,528
2012	1,528
2012.25	1,529
2012.5	1,528
2012.75	1,527
2013	1,527
2013.1666666666667	1,528
2013.4166666666667	1,528
2013.6666666666667	1,526
2013.9166666666667	1,526
2014.1666666666667	1,526
2014.3333333333333	1,525
2014.5833333333333	1,522
2014.8333333333333	1,521
2015.0833333333333	1,524
2015.25	1,525
2015.5	1,524
2015.75	1,521
2016	1,522
2016.25	1,527
2016.4166666666667	1,527
2016.6666666666667	1,525
2016.9166666666667	1,526
2017.1666666666667	1,527
2017.4166666666667	1,526
2017.5833333333333	1,525
2017.8333333333333	1,525
2018.0833333333333	1,525
2018.3333333333333	1,525
2018.5	1,524
2018.75	1,521
2019	1,522
2019.25	1,525
2019.5	1,525
2019.6666666666667	1,525
2019.9166666666667	1,525
2020.1666666666667	1,525
2020.4166666666667	1,525
2020.6666666666667	1,521
2020.8333333333333	1,521
2021.0833333333333	1,522
2021.3333333333333	1,523
2021.5833333333333	1,520
2021.75	1,520
2022	1,521
2022.25	1,523
2022.5	1,521
2022.75	1,520
2022.9166666666667	1,521
2023.1666666666667	1,523
2023.4166666666667	1,526
2023.6666666666667	1,525
2023.9166666666667	1,525
2024.0833333333333	1,526
2024.3333333333333	1,526
2024.5833333333333	1,525
2024.8333333333333	1,525
2025	1,526
2025.25	1,528
2025.5	1,528
2025.75	1,527
2026	1,528
2026.1666666666667	1,527
2026.4166666666667	1,526
2026.6666666666667	1,524

Rate and persistence

-0.67 Mm³

Mean drawdown per month over 12 months

4 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

Hyatt Reservoir

Gauge location

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 exist	Measured
Period held	1966–2026
Completeness	98.2% 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.
Continuity	98% of the months between 1966 and 2026 are held. Monthly means of the publisher's own daily record.
Last read from the publisher	2026-10-01
Redistribution	Permitted by the upstream licences
Commercial reuse	Permitted by the upstream licences. No Hydrionis access tier can widen this.
Methodology	How this was produced

Use this data

Machine-readable JSON /api/v1/observations/by-subject/reservoir-usbr-7183.json
How to cite this, and who you must credit
How these figures were produced
Request this at a different scale, format or geography

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), Hyatt Reservoir reservoir records, accessed 2026-10-05, hydrionis.com/reservoirs/reservoir-usbr-7183/

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 Hyatt 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

719 monthly observations 1966–2026 Mm³

Spatially aggregatedHigh confidenceSeptember 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 131063. 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.