Angostura Reservoir — storage

Storage now, against this reservoir's own record

64.10 Mm³

Stored, September 2026

3rd

Percentile among 75 Seps on record

-40.9%

Against the Sep 1991–2020 average

-17.6%

Change over the 12 months to 2026-09

Storage in September 2026 was lower than almost every other Sep on record, ranked against 75 other Seps held for this reservoir.

Storage, 1951–2026

Monthly mean storage

900 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 900 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 900 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
January 1959	145
April 1959	150
August 1959	123
December 1959	105
April 1960	123
July 1960	111
November 1960	86.6
March 1961	93.4
July 1961	93.8
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
August 1965	190
November 1965	178
March 1966	193
July 1966	176
November 1966	157
February 1967	166
June 1967	172
October 1967	138
February 1968	145
May 1968	160
September 1968	149
January 1969	149
May 1969	169
August 1969	163
December 1969	141
April 1970	162
August 1970	136
November 1970	120
March 1971	134
July 1971	164
November 1971	129
February 1972	137
June 1972	169
October 1972	128
February 1973	137
June 1973	167
September 1973	141
January 1974	160
May 1974	167
September 1974	110
December 1974	114
April 1975	141
August 1975	126
December 1975	111
March 1976	123
July 1976	134
November 1976	109
March 1977	118
June 1977	121
October 1977	91.6
February 1978	98.9
June 1978	171
September 1978	161
January 1979	162
May 1979	168
September 1979	162
January 1980	159
April 1980	170
August 1980	130
December 1980	121
April 1981	131
July 1981	112
November 1981	91.6
March 1982	105
July 1982	155
October 1982	142
February 1983	154
June 1983	159
October 1983	123
January 1984	130
May 1984	161
September 1984	119
January 1985	123
April 1985	138
August 1985	94.2
December 1985	86.9
April 1986	138
August 1986	142
November 1986	151
March 1987	160
July 1987	147
November 1987	116
February 1988	122
June 1988	120
October 1988	80.4
February 1989	86.2
May 1989	96.1
September 1989	70.4
January 1990	80.3
May 1990	98.1
August 1990	83.2
December 1990	78.7
April 1991	88.1
August 1991	140
November 1991	125
March 1992	137
July 1992	130
November 1992	103
March 1993	119
June 1993	159
October 1993	148
February 1994	152
June 1994	151
September 1994	107
January 1995	113
May 1995	144
September 1995	118
December 1995	121
April 1996	154
August 1996	125
December 1996	120
March 1997	160
July 1997	153
November 1997	146
March 1998	159
June 1998	159
October 1998	149
February 1999	157
June 1999	160
October 1999	134
January 2000	143
May 2000	159
September 2000	111
January 2001	117
April 2001	150
August 2001	140
December 2001	130
April 2002	144
July 2002	121
November 2002	98.6
March 2003	118
July 2003	132
October 2003	101
February 2004	111
June 2004	105
October 2004	68.1
January 2005	75.2
May 2005	87.1
September 2005	73.4
January 2006	70.3
May 2006	81.0
August 2006	55.3
December 2006	57.5
April 2007	67.4
August 2007	60.7
November 2007	61.5
March 2008	69.9
July 2008	101
November 2008	87.0
February 2009	93.8
June 2009	119
October 2009	92.7
February 2010	103
May 2010	133
September 2010	123
January 2011	128
May 2011	149
August 2011	131
December 2011	123
April 2012	144
August 2012	99.7
November 2012	90.8
March 2013	102
July 2013	100
November 2013	119
March 2014	145
June 2014	147
October 2014	129
February 2015	138
June 2015	142
September 2015	126
January 2016	135
May 2016	148
September 2016	110
December 2016	116
April 2017	138
August 2017	115
December 2017	109
March 2018	129
July 2018	142
November 2018	125
March 2019	138
June 2019	146
October 2019	132
February 2020	130
June 2020	137
October 2020	99.8
January 2021	109
May 2021	129
September 2021	94.4
January 2022	103
April 2022	115
August 2022	88.8
December 2022	80.9
April 2023	98.7
July 2023	125
November 2023	128
March 2024	135
July 2024	127
October 2024	99.0
February 2025	108
June 2025	111
October 2025	77.2
January 2026	86.2
May 2026	92.6
September 2026	64.1

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	67.0
Sep	108	64.1
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

900 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 900 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 900 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
1959	969
1959.25	969
1959.5833333333333	967
1959.9166666666667	966
1960.25	967
1960.5	966
1960.8333333333333	964
1961.1666666666667	965
1961.5	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
1965.5833333333333	971
1965.8333333333333	970
1966.1666666666667	971
1966.5	970
1966.8333333333333	971
1967.0833333333333	971
1967.4166666666667	972
1967.75	970
1968.0833333333333	970
1968.3333333333333	971
1968.6666666666667	970
1969	970
1969.3333333333333	971
1969.5833333333333	971
1969.9166666666667	970
1970.25	971
1970.5833333333333	969
1970.8333333333333	968
1971.1666666666667	969
1971.5	971
1971.8333333333333	969
1972.0833333333333	970
1972.4166666666667	971
1972.75	969
1973.0833333333333	970
1973.4166666666667	971
1973.6666666666667	970
1974	971
1974.3333333333333	971
1974.6666666666667	968
1974.9166666666667	968
1975.25	970
1975.5833333333333	969
1975.9166666666667	968
1976.1666666666667	969
1976.5	969
1976.8333333333333	968
1977.1666666666667	968
1977.4166666666667	969
1977.75	966
1978.0833333333333	967
1978.4166666666667	971
1978.6666666666667	971
1979	971
1979.3333333333333	971
1979.6666666666667	971
1980	971
1980.25	971
1980.5833333333333	969
1980.9166666666667	969
1981.25	969
1981.5	968
1981.8333333333333	967
1982.1666666666667	968
1982.5	971
1982.75	970
1983.0833333333333	971
1983.4166666666667	971
1983.75	969
1984	970
1984.3333333333333	971
1984.6666666666667	969
1985	969
1985.25	970
1985.5833333333333	967
1985.9166666666667	967
1986.25	970
1986.5833333333333	970
1986.8333333333333	971
1987.1666666666667	971
1987.5	971
1987.8333333333333	969
1988.0833333333333	969
1988.4166666666667	969
1988.75	966
1989.0833333333333	967
1989.3333333333333	967
1989.6666666666667	965
1990	966
1990.3333333333333	967
1990.5833333333333	966
1990.9166666666667	966
1991.25	967
1991.5833333333333	970
1991.8333333333333	969
1992.1666666666667	970
1992.5	970
1992.8333333333333	968
1993.1666666666667	969
1993.4166666666667	971
1993.75	971
1994.0833333333333	971
1994.4166666666667	971
1994.6666666666667	968
1995	969
1995.3333333333333	971
1995.6666666666667	969
1995.9166666666667	969
1996.25	971
1996.5833333333333	969
1996.9166666666667	969
1997.1666666666667	971
1997.5	971
1997.8333333333333	971
1998.1666666666667	971
1998.4166666666667	971
1998.75	971
1999.0833333333333	971
1999.4166666666667	971
1999.75	970
2000	970
2000.3333333333333	971
2000.6666666666667	968
2001	969
2001.25	971
2001.5833333333333	970
2001.9166666666667	970
2002.25	971
2002.5	969
2002.8333333333333	968
2003.1666666666667	969
2003.5	970
2003.75	968
2004.0833333333333	968
2004.4166666666667	968
2004.75	965
2005	966
2005.3333333333333	967
2005.6666666666667	965
2006	966
2006.3333333333333	967
2006.5833333333333	964
2006.9166666666667	965
2007.25	966
2007.5833333333333	965
2007.8333333333333	965
2008.1666666666667	966
2008.5	968
2008.8333333333333	967
2009.0833333333333	968
2009.4166666666667	970
2009.75	968
2010.0833333333333	968
2010.3333333333333	970
2010.6666666666667	970
2011	970
2011.3333333333333	971
2011.5833333333333	970
2011.9166666666667	970
2012.25	971
2012.5833333333333	968
2012.8333333333333	968
2013.1666666666667	968
2013.5	968
2013.8333333333333	970
2014.1666666666667	971
2014.4166666666667	971
2014.75	970
2015.0833333333333	971
2015.4166666666667	971
2015.6666666666667	970
2016	971
2016.3333333333333	971
2016.6666666666667	969
2016.9166666666667	969
2017.25	971
2017.5833333333333	969
2017.9166666666667	969
2018.1666666666667	970
2018.5	971
2018.8333333333333	970
2019.1666666666667	971
2019.4166666666667	971
2019.75	970
2020.0833333333333	970
2020.4166666666667	971
2020.75	968
2021	969
2021.3333333333333	970
2021.6666666666667	968
2022	969
2022.25	969
2022.5833333333333	967
2022.9166666666667	967
2023.25	968
2023.5	970
2023.8333333333333	970
2024.1666666666667	971
2024.5	970
2024.75	968
2025.0833333333333	969
2025.4166666666667	969
2025.75	966
2026	967
2026.3333333333333	968
2026.6666666666667	965

Rate and persistence

-1.14 Mm³

Mean drawdown per month over 12 months

18 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	98.7% 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.
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	2026-10-01
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-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 2026-10-05, 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

900 monthly observations 1951–2026 Mm³

Spatially aggregatedHigh confidenceSeptember 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 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.