Fourmile Lake And Fourmile Lake — storage

Storage now, against this reservoir's own record

1.35 Mm³

Stored, August 2026

3rd

Percentile among 35 Augs on record

-83.2%

Against the Aug 1991–2020 average

-63.5%

Change over the 12 months to 2026-08

Storage in August 2026 was lower than almost every other Aug on record, ranked against 35 other Augs held for this reservoir.

Storage, 1991–2026

Monthly mean storage

417 monthly values, 1991 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 417 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 417 would be longer than this page and unusable with a screen reader.
Period	Fourmile Lake And Fourmile Lake (Mm³)
November 1991	6.41
January 1992	5.16
February 1992	5.45
April 1992	6.94
June 1992	6.04
August 1992	4.14
September 1992	4.05
November 1992	5.17
January 1993	6.23
March 1993	7.23
April 1993	9.10
June 1993	18.7
August 1993	13.9
October 1993	10.7
November 1993	10.6
January 1994	11.4
March 1994	11.5
May 1994	13.5
June 1994	13.5
August 1994	3.80
October 1994	2.57
December 1994	4.41
January 1995	5.34
March 1995	7.12
May 1995	9.31
July 1995	15.7
August 1995	13.9
October 1995	11.1
December 1995	13.8
January 1996	18.0
March 1996	18.3
May 1996	20.9
July 1996	17.2
August 1996	13.9
October 1996	12.1
December 1996	17.2
February 1997	17.8
March 1997	17.7
May 1997	20.9
July 1997	18.2
September 1997	14.3
October 1997	14.4
December 1997	15.4
February 1998	17.6
April 1998	17.9
May 1998	19.6
July 1998	19.0
September 1998	12.9
November 1998	12.6
December 1998	14.6
February 1999	16.7
April 1999	17.8
June 1999	18.1
July 1999	18.4
September 1999	11.0
November 1999	9.59
December 1999	10.3
February 2000	11.9
April 2000	14.2
June 2000	18.3
July 2000	15.3
September 2000	8.05
November 2000	8.18
January 2001	8.70
February 2001	8.96
April 2001	10.6
June 2001	10.4
August 2001	3.37
September 2001	2.19
November 2001	2.15
January 2002	3.28
March 2002	4.77
April 2002	5.58
June 2002	10.2
August 2002	3.40
October 2002	1.57
November 2002	1.28
January 2003	1.52
March 2003	3.91
May 2003	6.64
June 2003	9.52
August 2003	2.87
October 2003	1.48
November 2003	1.42
January 2004	2.64
March 2004	2.73
May 2004	7.69
June 2004	10.5
August 2004	3.50
October 2004	1.99
December 2004	3.08
January 2005	3.52
March 2005	3.89
May 2005	7.07
July 2005	6.58
August 2005	2.71
October 2005	1.59
December 2005	4.10
February 2006	6.77
March 2006	6.81
May 2006	11.5
July 2006	15.3
September 2006	8.93
October 2006	8.76
December 2006	11.2
February 2007	12.6
April 2007	16.1
May 2007	17.3
July 2007	15.4
September 2007	8.33
October 2007	8.57
December 2007	10.1
February 2008	12.5
April 2008	13.9
May 2008	15.9
July 2008	18.7
September 2008	11.8
November 2008	11.2
December 2008	11.8
February 2009	14.1
April 2009	15.9
June 2009	19.8
July 2009	16.4
September 2009	9.65
November 2009	8.95
January 2010	9.95
February 2010	10.4
April 2010	11.5
June 2010	16.3
August 2010	9.75
September 2010	6.35
November 2010	6.01
January 2011	8.72
February 2011	9.90
April 2011	12.5
June 2011	17.5
August 2011	15.1
September 2011	13.0
November 2011	12.2
January 2012	12.9
March 2012	15.3
April 2012	16.9
June 2012	18.8
August 2012	12.6
October 2012	6.51
November 2012	6.74
January 2013	9.79
March 2013	10.7
May 2013	13.3
June 2013	10.7
August 2013	5.22
October 2013	2.54
December 2013	3.09
January 2014	3.42
March 2014	7.36
May 2014	8.79
July 2014	1.99
August 2014	1.86
October 2014	1.86
December 2014	3.23
January 2015	5.84
March 2015	8.44
May 2015	9.67
July 2015	3.04
August 2015	0.531
October 2015	0
December 2015	2.25
February 2016	4.42
March 2016	5.51
May 2016	10.5
July 2016	6.07
October 2016	1.92
November 2016	2.47
January 2017	3.95
March 2017	5.97
May 2017	10.9
June 2017	13.8
August 2017	6.24
October 2017	4.96
December 2017	6.72
January 2018	7.37
March 2018	8.78
May 2018	10.7
July 2018	4.36
August 2018	2.50
October 2018	1.94
December 2018	2.61
January 2019	3.39
March 2019	5.09
May 2019	10.1
July 2019	6.15
August 2019	3.01
October 2019	1.94
December 2019	2.22
February 2020	4.04
March 2020	4.47
May 2020	7.50
July 2020	3.66
September 2020	1.86
October 2020	1.86
December 2020	2.21
February 2021	3.57
April 2021	4.59
May 2021	5.89
July 2021	2.20
September 2021	1.86
November 2021	1.86
December 2021	1.92
February 2022	2.78
April 2022	4.01
June 2022	7.47
July 2022	4.32
September 2022	2.04
November 2022	2.28
December 2022	2.69
February 2023	4.57
April 2023	6.07
June 2023	11.5
July 2023	7.60
September 2023	1.89
November 2023	1.92
January 2024	3.87
February 2024	5.20
April 2024	6.98
June 2024	9.78
August 2024	2.65
September 2024	1.95
November 2024	2.63
January 2025	5.41
March 2025	7.16
April 2025	8.64
June 2025	12.9
August 2025	3.70
October 2025	1.68
November 2025	1.89
January 2026	4.43
March 2026	6.33
May 2026	3.68
June 2026	1.62
August 2026	1.35

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	8.36	4.43
Feb	9.07	4.91
Mar	9.74	6.33
Apr	10.9	6.60
May	12.9	3.68
Jun	13.7	1.62
Jul	11.3	1.34
Aug	8.03	1.35
Sep	6.37	1.84
Oct	5.87	1.68
Nov	6.28	1.89
Dec	7.19	2.72

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

417 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 417 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 417 would be longer than this page and unusable with a screen reader.
Period	Fourmile Lake And Fourmile Lake (m)
1991.8333333333333	1,747
1992	1,747
1992.0833333333333	1,747
1992.25	1,748
1992.4166666666667	1,747
1992.5833333333333	1,746
1992.6666666666667	1,746
1992.8333333333333	1,747
1993	1,747
1993.1666666666667	1,748
1993.25	1,748
1993.4166666666667	1,751
1993.5833333333333	1,750
1993.75	1,749
1993.8333333333333	1,749
1994	1,749
1994.1666666666667	1,749
1994.3333333333333	1,750
1994.4166666666667	1,750
1994.5833333333333	1,746
1994.75	1,746
1994.9166666666667	1,747
1995	1,747
1995.1666666666667	1,748
1995.3333333333333	1,749
1995.5	1,751
1995.5833333333333	1,750
1995.75	1,749
1995.9166666666667	1,750
1996	1,751
1996.1666666666667	1,751
1996.3333333333333	1,752
1996.5	1,751
1996.5833333333333	1,750
1996.75	1,749
1996.9166666666667	1,751
1997.0833333333333	1,751
1997.1666666666667	1,751
1997.3333333333333	1,752
1997.5	1,751
1997.6666666666667	1,750
1997.75	1,750
1997.9166666666667	1,750
1998.0833333333333	1,751
1998.25	1,751
1998.3333333333333	1,752
1998.5	1,751
1998.6666666666667	1,750
1998.8333333333333	1,750
1998.9166666666667	1,750
1999.0833333333333	1,751
1999.25	1,751
1999.4166666666667	1,751
1999.5	1,751
1999.6666666666667	1,749
1999.8333333333333	1,749
1999.9166666666667	1,749
2000.0833333333333	1,749
2000.25	1,750
2000.4166666666667	1,751
2000.5	1,750
2000.6666666666667	1,748
2000.8333333333333	1,748
2001	1,748
2001.0833333333333	1,748
2001.25	1,749
2001.4166666666667	1,749
2001.5833333333333	1,746
2001.6666666666667	1,746
2001.8333333333333	1,746
2002	1,746
2002.1666666666667	1,747
2002.25	1,747
2002.4166666666667	1,749
2002.5833333333333	1,746
2002.75	1,745
2002.8333333333333	1,745
2003	1,745
2003.1666666666667	1,746
2003.3333333333333	1,748
2003.4166666666667	1,749
2003.5833333333333	1,746
2003.75	1,745
2003.8333333333333	1,745
2004	1,746
2004.1666666666667	1,746
2004.3333333333333	1,748
2004.4166666666667	1,749
2004.5833333333333	1,746
2004.75	1,746
2004.9166666666667	1,746
2005	1,746
2005.1666666666667	1,746
2005.3333333333333	1,748
2005.5	1,747
2005.5833333333333	1,746
2005.75	1,745
2005.9166666666667	1,746
2006.0833333333333	1,748
2006.1666666666667	1,748
2006.3333333333333	1,749
2006.5	1,750
2006.6666666666667	1,748
2006.75	1,748
2006.9166666666667	1,749
2007.0833333333333	1,750
2007.25	1,751
2007.3333333333333	1,751
2007.5	1,750
2007.6666666666667	1,748
2007.75	1,748
2007.9166666666667	1,749
2008.0833333333333	1,750
2008.25	1,750
2008.3333333333333	1,751
2008.5	1,751
2008.6666666666667	1,749
2008.8333333333333	1,749
2008.9166666666667	1,749
2009.0833333333333	1,750
2009.25	1,751
2009.4166666666667	1,752
2009.5	1,751
2009.6666666666667	1,749
2009.8333333333333	1,748
2010	1,749
2010.0833333333333	1,749
2010.25	1,749
2010.4166666666667	1,751
2010.5833333333333	1,749
2010.6666666666667	1,747
2010.8333333333333	1,747
2011	1,748
2011.0833333333333	1,749
2011.25	1,750
2011.4166666666667	1,751
2011.5833333333333	1,750
2011.6666666666667	1,750
2011.8333333333333	1,750
2012	1,750
2012.1666666666667	1,750
2012.25	1,751
2012.4166666666667	1,751
2012.5833333333333	1,750
2012.75	1,747
2012.8333333333333	1,748
2013	1,749
2013.1666666666667	1,749
2013.3333333333333	1,750
2013.4166666666667	1,749
2013.5833333333333	1,747
2013.75	1,746
2013.9166666666667	1,746
2014	1,746
2014.1666666666667	1,748
2014.3333333333333	1,748
2014.5	1,746
2014.5833333333333	1,746
2014.75	1,746
2014.9166666666667	1,746
2015	1,747
2015.1666666666667	1,748
2015.3333333333333	1,749
2015.5	1,746
2015.5833333333333	1,745
2015.75	1,745
2015.9166666666667	1,746
2016.0833333333333	1,747
2016.1666666666667	1,747
2016.3333333333333	1,749
2016.5	1,747
2016.75	1,746
2016.8333333333333	1,746
2017	1,746
2017.1666666666667	1,747
2017.3333333333333	1,749
2017.4166666666667	1,750
2017.5833333333333	1,747
2017.75	1,747
2017.9166666666667	1,748
2018	1,748
2018.1666666666667	1,748
2018.3333333333333	1,749
2018.5	1,747
2018.5833333333333	1,746
2018.75	1,746
2018.9166666666667	1,746
2019	1,746
2019.1666666666667	1,747
2019.3333333333333	1,749
2019.5	1,747
2019.5833333333333	1,746
2019.75	1,746
2019.9166666666667	1,746
2020.0833333333333	1,746
2020.1666666666667	1,747
2020.3333333333333	1,748
2020.5	1,746
2020.6666666666667	1,746
2020.75	1,746
2020.9166666666667	1,746
2021.0833333333333	1,746
2021.25	1,747
2021.3333333333333	1,747
2021.5	1,746
2021.6666666666667	1,746
2021.8333333333333	1,746
2021.9166666666667	1,746
2022.0833333333333	1,746
2022.25	1,746
2022.4166666666667	1,748
2022.5	1,747
2022.6666666666667	1,746
2022.8333333333333	1,746
2022.9166666666667	1,746
2023.0833333333333	1,747
2023.25	1,747
2023.4166666666667	1,749
2023.5	1,748
2023.6666666666667	1,746
2023.8333333333333	1,746
2024	1,746
2024.0833333333333	1,747
2024.25	1,748
2024.4166666666667	1,749
2024.5833333333333	1,746
2024.6666666666667	1,746
2024.8333333333333	1,746
2025	1,747
2025.1666666666667	1,748
2025.25	1,748
2025.4166666666667	1,750
2025.5833333333333	1,746
2025.75	1,745
2025.8333333333333	1,746
2026	1,747
2026.1666666666667	1,747
2026.3333333333333	1,746
2026.4166666666667	1,745
2026.5833333333333	1,745

Rate and persistence

-0.20 Mm³

Mean drawdown per month over 12 months

7 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

Fourmile Lake And Fourmile Lake

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	1991–2026
Completeness	96.5% 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	97% of the months between 1991 and 2026 are held. Monthly means of the publisher's own daily record.
Last read from the publisher	2026-09-01
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-7177.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), Fourmile Lake And Fourmile Lake reservoir records, accessed 2026-09-02, hydrionis.com/reservoirs/reservoir-usbr-7177/

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 Fourmile Lake And Fourmile Lake 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

417 monthly observations 1991–2026 Mm³

Spatially aggregatedHigh confidenceAugust 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 130544. 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.