Angostura Reservoir — storage

Storage now, against this reservoir's own record

67.12 Mm³

Stored, August 2026

3rd

Percentile among 75 Augs on record

-42.9%

Against the Aug 1991–2020 average

-25.0%

Change over the 12 months to 2026-08

Storage in August 2026 was lower than almost every other Aug on record, ranked against 75 other Augs held for this reservoir.

Storage, 1951–2026

Monthly mean storage

899 monthly values, 1951 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 899 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 899 would be longer than this page and unusable with a screen reader.
Period	Angostura Reservoir (Mm³)
October 1951	0
February 1952	0
June 1952	168
September 1952	177
January 1953	143
May 1953	143
September 1953	131
December 1953	126
April 1954	128
August 1954	132
December 1954	124
March 1955	138
July 1955	188
November 1955	189
March 1956	182
June 1956	176
October 1956	113
February 1957	119
June 1957	197
September 1957	166
January 1958	158
May 1958	170
September 1958	168
December 1958	148
April 1959	150
August 1959	123
December 1959	105
March 1960	114
July 1960	111
November 1960	86.6
March 1961	93.4
June 1961	96.9
October 1961	88.0
February 1962	96.1
June 1962	199
October 1962	173
January 1963	177
May 1963	197
September 1963	170
January 1964	170
April 1964	181
August 1964	168
December 1964	150
April 1965	169
July 1965	197
November 1965	178
March 1966	193
July 1966	176
October 1966	154
February 1967	166
June 1967	172
October 1967	138
January 1968	142
May 1968	160
September 1968	149
January 1969	149
April 1969	167
August 1969	163
December 1969	141
April 1970	162
July 1970	155
November 1970	120
March 1971	134
July 1971	164
October 1971	127
February 1972	137
June 1972	169
October 1972	128
January 1973	134
May 1973	169
September 1973	141
January 1974	160
May 1974	167
August 1974	119
December 1974	114
April 1975	141
August 1975	126
November 1975	109
March 1976	123
July 1976	134
November 1976	109
February 1977	114
June 1977	121
October 1977	91.6
February 1978	98.9
May 1978	172
September 1978	161
January 1979	162
May 1979	168
August 1979	162
December 1979	158
April 1980	170
August 1980	130
November 1980	119
March 1981	130
July 1981	112
November 1981	91.6
February 1982	97.7
June 1982	155
October 1982	142
February 1983	154
May 1983	161
September 1983	126
January 1984	130
May 1984	161
September 1984	119
December 1984	121
April 1985	138
August 1985	94.2
December 1985	86.9
March 1986	123
July 1986	156
November 1986	151
March 1987	160
June 1987	159
October 1987	115
February 1988	122
June 1988	120
September 1988	81.4
January 1989	84.6
May 1989	96.1
September 1989	70.4
December 1989	78.5
April 1990	94.0
August 1990	83.2
December 1990	78.7
March 1991	85.5
July 1991	156
November 1991	125
March 1992	137
June 1992	134
October 1992	101
February 1993	108
June 1993	159
September 1993	148
January 1994	147
May 1994	158
September 1994	107
January 1995	113
April 1995	130
August 1995	134
December 1995	121
April 1996	154
July 1996	145
November 1996	117
March 1997	160
July 1997	153
October 1997	144
February 1998	155
June 1998	159
October 1998	149
January 1999	150
May 1999	160
September 1999	134
January 2000	143
April 2000	160
August 2000	123
December 2000	115
April 2001	150
July 2001	152
November 2001	128
March 2002	138
July 2002	121
October 2002	96.7
February 2003	107
June 2003	138
October 2003	101
January 2004	108
May 2004	115
September 2004	67.5
January 2005	75.2
May 2005	87.1
August 2005	84.1
December 2005	67.6
April 2006	79.8
August 2006	55.3
November 2006	55.9
March 2007	64.9
July 2007	61.1
November 2007	61.5
February 2008	66.3
June 2008	106
October 2008	85.9
February 2009	93.8
May 2009	118
September 2009	93.6
January 2010	100
May 2010	133
August 2010	135
December 2010	125
April 2011	147
August 2011	131
November 2011	120
March 2012	138
July 2012	117
November 2012	90.8
February 2013	98.1
June 2013	108
October 2013	104
February 2014	132
May 2014	148
September 2014	118
January 2015	133
May 2015	146
August 2015	136
December 2015	133
April 2016	146
August 2016	117
December 2016	116
March 2017	131
July 2017	131
November 2017	106
March 2018	129
June 2018	146
October 2018	125
February 2019	127
June 2019	146
September 2019	129
January 2020	128
May 2020	142
September 2020	100.0
December 2020	106
April 2021	126
August 2021	104
December 2021	101
March 2022	110
July 2022	105
November 2022	78.5
March 2023	90.3
June 2023	117
October 2023	120
February 2024	132
June 2024	141
September 2024	101
January 2025	106
May 2025	112
September 2025	77.8
December 2025	83.3
April 2026	94.0
August 2026	67.1

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	114	86.2
Feb	118	88.7
Mar	125	91.8
Apr	131	94.0
May	135	92.6
Jun	137	87.7
Jul	129	78.7
Aug	118	67.1
Sep	108	77.8
Oct	109	77.2
Nov	111	80.5
Dec	112	83.3

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

899 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 899 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 899 would be longer than this page and unusable with a screen reader.
Period	Angostura Reservoir (m)
1951.75	0
1952.0833333333333	0
1952.4166666666667	970
1952.6666666666667	970
1953	968
1953.3333333333333	968
1953.6666666666667	968
1953.9166666666667	967
1954.25	967
1954.5833333333333	968
1954.9166666666667	967
1955.1666666666667	968
1955.5	971
1955.8333333333333	971
1956.1666666666667	971
1956.4166666666667	970
1956.75	966
1957.0833333333333	967
1957.4166666666667	971
1957.6666666666667	970
1958	969
1958.3333333333333	970
1958.6666666666667	970
1958.9166666666667	969
1959.25	969
1959.5833333333333	967
1959.9166666666667	966
1960.1666666666667	966
1960.5	966
1960.8333333333333	964
1961.1666666666667	965
1961.4166666666667	965
1961.75	964
1962.0833333333333	965
1962.4166666666667	972
1962.75	970
1963	970
1963.3333333333333	971
1963.6666666666667	970
1964	970
1964.25	971
1964.5833333333333	970
1964.9166666666667	969
1965.25	970
1965.5	971
1965.8333333333333	970
1966.1666666666667	971
1966.5	970
1966.75	971
1967.0833333333333	971
1967.4166666666667	972
1967.75	970
1968	970
1968.3333333333333	971
1968.6666666666667	970
1969	970
1969.25	971
1969.5833333333333	971
1969.9166666666667	970
1970.25	971
1970.5	971
1970.8333333333333	968
1971.1666666666667	969
1971.5	971
1971.75	969
1972.0833333333333	970
1972.4166666666667	971
1972.75	969
1973	969
1973.3333333333333	971
1973.6666666666667	970
1974	971
1974.3333333333333	971
1974.5833333333333	968
1974.9166666666667	968
1975.25	970
1975.5833333333333	969
1975.8333333333333	968
1976.1666666666667	969
1976.5	969
1976.8333333333333	968
1977.0833333333333	968
1977.4166666666667	969
1977.75	966
1978.0833333333333	967
1978.3333333333333	971
1978.6666666666667	971
1979	971
1979.3333333333333	971
1979.5833333333333	971
1979.9166666666667	971
1980.25	971
1980.5833333333333	969
1980.8333333333333	968
1981.1666666666667	969
1981.5	968
1981.8333333333333	967
1982.0833333333333	967
1982.4166666666667	971
1982.75	970
1983.0833333333333	971
1983.3333333333333	971
1983.6666666666667	969
1984	970
1984.3333333333333	971
1984.6666666666667	969
1984.9166666666667	969
1985.25	970
1985.5833333333333	967
1985.9166666666667	967
1986.1666666666667	969
1986.5	971
1986.8333333333333	971
1987.1666666666667	971
1987.4166666666667	971
1987.75	969
1988.0833333333333	969
1988.4166666666667	969
1988.6666666666667	966
1989	966
1989.3333333333333	967
1989.6666666666667	965
1989.9166666666667	966
1990.25	967
1990.5833333333333	966
1990.9166666666667	966
1991.1666666666667	966
1991.5	971
1991.8333333333333	969
1992.1666666666667	970
1992.4166666666667	970
1992.75	968
1993.0833333333333	968
1993.4166666666667	971
1993.6666666666667	971
1994	971
1994.3333333333333	971
1994.6666666666667	968
1995	969
1995.25	970
1995.5833333333333	970
1995.9166666666667	969
1996.25	971
1996.5	971
1996.8333333333333	969
1997.1666666666667	971
1997.5	971
1997.75	971
1998.0833333333333	971
1998.4166666666667	971
1998.75	971
1999	971
1999.3333333333333	971
1999.6666666666667	970
2000	970
2000.25	971
2000.5833333333333	969
2000.9166666666667	969
2001.25	971
2001.5	971
2001.8333333333333	970
2002.1666666666667	970
2002.5	969
2002.75	967
2003.0833333333333	968
2003.4166666666667	970
2003.75	968
2004	968
2004.3333333333333	969
2004.6666666666667	965
2005	966
2005.3333333333333	967
2005.5833333333333	966
2005.9166666666667	966
2006.25	967
2006.5833333333333	964
2006.8333333333333	964
2007.1666666666667	965
2007.5	965
2007.8333333333333	965
2008.0833333333333	966
2008.4166666666667	969
2008.75	967
2009.0833333333333	968
2009.3333333333333	969
2009.6666666666667	968
2010	968
2010.3333333333333	970
2010.5833333333333	971
2010.9166666666667	970
2011.25	971
2011.5833333333333	970
2011.8333333333333	970
2012.1666666666667	971
2012.5	969
2012.8333333333333	968
2013.0833333333333	968
2013.4166666666667	969
2013.75	969
2014.0833333333333	970
2014.3333333333333	971
2014.6666666666667	970
2015	970
2015.3333333333333	971
2015.5833333333333	971
2015.9166666666667	970
2016.25	971
2016.5833333333333	969
2016.9166666666667	969
2017.1666666666667	970
2017.5	970
2017.8333333333333	969
2018.1666666666667	970
2018.4166666666667	971
2018.75	970
2019.0833333333333	970
2019.4166666666667	971
2019.6666666666667	970
2020	970
2020.3333333333333	971
2020.6666666666667	968
2020.9166666666667	969
2021.25	970
2021.5833333333333	969
2021.9166666666667	968
2022.1666666666667	969
2022.5	969
2022.8333333333333	967
2023.1666666666667	968
2023.4166666666667	969
2023.75	970
2024.0833333333333	970
2024.4166666666667	971
2024.6666666666667	968
2025	969
2025.3333333333333	969
2025.6666666666667	967
2025.9166666666667	967
2026.25	968
2026.5833333333333	966

Rate and persistence

-1.87 Mm³

Mean drawdown per month over 12 months

17 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

Angostura 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	1951–2026
Completeness	98.6% 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.
Continuity	99% of the months between 1951 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-257.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), Angostura Reservoir reservoir records, accessed 2026-09-02, hydrionis.com/reservoirs/reservoir-usbr-257/

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 Angostura 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

899 monthly observations 1951–2026 Mm³

Spatially aggregatedHigh confidenceAugust 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 105. 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.