Island Park Reservoir — storage

Storage now, against this reservoir's own record

29.37 Mm³

Stored, September 2026

17th

Percentile among 88 Seps on record

-64.5%

Against the Sep 1991–2020 average

-46.6%

Change over the 12 months to 2026-09

Storage in September 2026 was lower than most Seps on record, ranked against 88 other Seps held for this reservoir.

Storage, 1938–2026

Monthly mean storage

1,054 monthly values, 1938 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 1,054 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 1,054 would be longer than this page and unusable with a screen reader.
Period	Island Park Reservoir (Mm³)
December 1938	28.1
April 1939	138
September 1939	68.8
January 1940	118
June 1940	162
October 1940	21.3
February 1941	97.8
July 1941	131
November 1941	52.5
April 1942	160
August 1942	102
December 1942	107
May 1943	167
September 1943	117
February 1944	164
June 1944	167
October 1944	64.1
March 1945	163
July 1945	163
December 1945	104
April 1946	164
September 1946	66.5
January 1947	107
May 1947	167
October 1947	93.8
February 1948	163
July 1948	145
November 1948	47.9
March 1949	129
August 1949	79.1
December 1949	69.6
May 1950	159
September 1950	111
January 1951	143
June 1951	167
October 1951	100
March 1952	94.1
July 1952	157
November 1952	82.9
April 1953	139
August 1953	101
January 1954	98.6
May 1954	168
September 1954	70.1
February 1955	147
June 1955	168
November 1955	54.9
March 1956	135
July 1956	149
December 1956	110
April 1957	153
September 1957	69.2
January 1958	130
June 1958	165
October 1958	26.9
February 1959	133
July 1959	138
November 1959	50.8
April 1960	167
August 1960	46.6
December 1960	46.2
May 1961	166
September 1961	16.7
February 1962	92.7
June 1962	168
October 1962	79.8
March 1963	164
July 1963	134
December 1963	73.7
April 1964	163
August 1964	117
January 1965	137
May 1965	171
October 1965	120
February 1966	140
June 1966	156
November 1966	45.5
March 1967	129
August 1967	128
December 1967	132
April 1968	163
September 1968	109
January 1969	133
June 1969	168
October 1969	64.2
February 1970	162
July 1970	162
November 1970	95.4
April 1971	164
August 1971	146
January 1972	110
May 1972	171
September 1972	112
February 1973	121
June 1973	167
November 1973	91.8
March 1974	145
July 1974	164
December 1974	128
April 1975	147
September 1975	130
January 1976	129
May 1976	145
October 1976	78.0
February 1977	143
July 1977	102
November 1977	48.6
March 1978	126
August 1978	123
December 1978	142
May 1979	135
September 1979	6.62
January 1980	97.9
June 1980	167
October 1980	78.5
March 1981	155
July 1981	127
November 1981	54.0
April 1982	151
August 1982	134
January 1983	135
May 1983	158
October 1983	75.4
February 1984	137
June 1984	167
November 1984	57.3
March 1985	123
August 1985	94.0
December 1985	116
April 1986	152
September 1986	125
January 1987	131
June 1987	162
October 1987	69.5
February 1988	136
July 1988	100.0
November 1988	53.0
April 1989	122
August 1989	91.5
December 1989	128
May 1990	165
September 1990	71.4
February 1991	108
June 1991	165
October 1991	75.7
March 1992	129
July 1992	88.3
December 1992	59.9
April 1993	122
August 1993	141
January 1994	152
May 1994	166
October 1994	55.5
February 1995	111
July 1995	166
November 1995	135
March 1996	144
August 1996	144
December 1996	147
May 1997	155
September 1997	158
January 1998	138
June 1998	167
October 1998	143
March 1999	137
July 1999	164
November 1999	141
April 2000	154
August 2000	94.0
January 2001	137
May 2001	164
September 2001	24.7
February 2002	110
June 2002	152
November 2002	43.3
March 2003	113
July 2003	110
December 2003	74.0
April 2004	127
September 2004	42.8
January 2005	93.1
May 2005	159
October 2005	67.1
February 2006	117
July 2006	149
November 2006	115
March 2007	147
August 2007	53.7
December 2007	80.4
May 2008	159
September 2008	89.5
February 2009	139
June 2009	159
October 2009	106
March 2010	141
July 2010	143
December 2010	111
April 2011	128
August 2011	163
January 2012	136
May 2012	164
October 2012	77.0
February 2013	126
June 2013	158
November 2013	73.0
March 2014	122
August 2014	94.5
December 2014	120
April 2015	163
September 2015	49.5
January 2016	111
June 2016	156
October 2016	46.4
February 2017	115
July 2017	162
November 2017	141
April 2018	149
August 2018	130
December 2018	148
May 2019	148
September 2019	122
February 2020	147
June 2020	167
November 2020	119
March 2021	148
July 2021	102
December 2021	120
April 2022	155
September 2022	78.2
January 2023	124
May 2023	154
October 2023	117
February 2024	151
July 2024	127
November 2024	110
March 2025	146
August 2025	62.9
December 2025	99.2
May 2026	160
September 2026	29.4

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	121	114
Feb	127	124
Mar	132	135
Apr	143	155
May	159	160
Jun	160	138
Jul	135	92.5
Aug	99.7	59.5
Sep	82.7	29.4
Oct	88.2	64.3
Nov	102	83.2
Dec	114	99.2

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

912 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 912 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 912 would be longer than this page and unusable with a screen reader.
Period	Island Park Reservoir (m)
1950.75	1,919
1951.0833333333333	1,920
1951.4166666666667	1,921
1951.6666666666667	1,920
1952	1,919
1952.3333333333333	1,921
1952.6666666666667	1,918
1953	1,920
1953.25	1,920
1953.5833333333333	1,919
1953.9166666666667	1,917
1954.25	1,921
1954.5833333333333	1,919
1954.9166666666667	1,918
1955.1666666666667	1,921
1955.5	1,921
1955.8333333333333	1,916
1956.1666666666667	1,920
1956.5	1,921
1956.75	1,919
1957.0833333333333	1,921
1957.4166666666667	1,921
1957.75	1,917
1958.0833333333333	1,920
1958.3333333333333	1,921
1958.6666666666667	1,913
1959	1,919
1959.3333333333333	1,921
1959.6666666666667	1,914
1960	1,919
1960.25	1,921
1960.5833333333333	1,916
1960.9166666666667	1,916
1961.25	1,921
1961.5833333333333	1,915
1961.8333333333333	1,913
1962.1666666666667	1,919
1962.5	1,921
1962.8333333333333	1,918
1963.1666666666667	1,921
1963.4166666666667	1,921
1963.75	1,915
1964.0833333333333	1,920
1964.4166666666667	1,921
1964.75	1,918
1965.0833333333333	1,921
1965.3333333333333	1,921
1965.6666666666667	1,920
1966	1,920
1966.3333333333333	1,921
1966.6666666666667	1,912
1966.9166666666667	1,916
1967.25	1,921
1967.5833333333333	1,920
1967.9166666666667	1,920
1968.25	1,921
1968.5	1,921
1968.8333333333333	1,920
1969.1666666666667	1,920
1969.5	1,921
1969.8333333333333	1,917
1970.1666666666667	1,921
1970.4166666666667	1,921
1970.75	1,918
1971.0833333333333	1,920
1971.4166666666667	1,921
1971.75	1,919
1972	1,919
1972.3333333333333	1,921
1972.6666666666667	1,919
1973	1,919
1973.3333333333333	1,921
1973.5833333333333	1,920
1973.9166666666667	1,919
1974.25	1,920
1974.5833333333333	1,921
1974.9166666666667	1,920
1975.25	1,921
1975.5	1,921
1975.8333333333333	1,920
1976.1666666666667	1,919
1976.5	1,921
1976.8333333333333	1,919
1977.0833333333333	1,920
1977.4166666666667	1,921
1977.75	1,913
1978.0833333333333	1,919
1978.4166666666667	1,921
1978.6666666666667	1,919
1979	1,920
1979.3333333333333	1,920
1979.6666666666667	1,907
1980	1,919
1980.25	1,921
1980.5833333333333	1,918
1980.9166666666667	1,920
1981.25	1,921
1981.5833333333333	1,917
1981.9166666666667	1,918
1982.1666666666667	1,920
1982.5	1,921
1982.8333333333333	1,920
1983.1666666666667	1,920
1983.5	1,921
1983.75	1,918
1984.0833333333333	1,920
1984.4166666666667	1,921
1984.75	1,914
1985.0833333333333	1,919
1985.3333333333333	1,921
1985.6666666666667	1,918
1986	1,919
1986.3333333333333	1,921
1986.6666666666667	1,920
1987	1,920
1987.25	1,921
1987.5833333333333	1,918
1987.9166666666667	1,919
1988.25	1,921
1988.5833333333333	1,916
1988.8333333333333	1,916
1989.1666666666667	1,919
1989.5	1,920
1989.8333333333333	1,919
1990.1666666666667	1,921
1990.4166666666667	1,921
1990.75	1,918
1991.0833333333333	1,919
1991.4166666666667	1,921
1991.75	1,918
1992.0833333333333	1,920
1992.3333333333333	1,921
1992.6666666666667	1,905
1993	1,918
1993.3333333333333	1,920
1993.6666666666667	1,920
1993.9166666666667	1,921
1994.25	1,921
1994.5833333333333	1,916
1994.9166666666667	1,918
1995.25	1,920
1995.5	1,921
1995.8333333333333	1,920
1996.1666666666667	1,920
1996.5	1,921
1996.8333333333333	1,920
1997.1666666666667	1,920
1997.4166666666667	1,921
1997.75	1,921
1998.0833333333333	1,920
1998.4166666666667	1,921
1998.75	1,920
1999	1,920
1999.3333333333333	1,921
1999.6666666666667	1,921
2000	1,920
2000.3333333333333	1,921
2000.5833333333333	1,919
2000.9166666666667	1,920
2001.25	1,921
2001.5833333333333	1,916
2001.9166666666667	1,918
2002.1666666666667	1,920
2002.5	1,919
2002.8333333333333	1,915
2003.1666666666667	1,919
2003.5	1,919
2003.8333333333333	1,916
2004.0833333333333	1,919
2004.4166666666667	1,921
2004.75	1,916
2005.0833333333333	1,919
2005.4166666666667	1,921
2005.6666666666667	1,917
2006	1,919
2006.3333333333333	1,921
2006.6666666666667	1,918
2007	1,920
2007.25	1,921
2007.5833333333333	1,916
2007.9166666666667	1,918
2008.25	1,920
2008.5833333333333	1,919
2008.9166666666667	1,920
2009.1666666666667	1,921
2009.5	1,921
2009.8333333333333	1,920
2010.1666666666667	1,920
2010.5	1,920
2010.75	1,918
2011.0833333333333	1,919
2011.4166666666667	1,921
2011.75	1,920
2012.0833333333333	1,920
2012.3333333333333	1,921
2012.6666666666667	1,917
2013	1,920
2013.3333333333333	1,921
2013.6666666666667	1,916
2014	1,919
2014.25	1,920
2014.5833333333333	1,919
2014.9166666666667	1,920
2015.25	1,921
2015.5833333333333	1,917
2015.8333333333333	1,918
2016.1666666666667	1,920
2016.5	1,918
2016.8333333333333	1,917
2017.1666666666667	1,920
2017.4166666666667	1,921
2017.75	1,920
2018.0833333333333	1,921
2018.4166666666667	1,921
2018.75	1,920
2019.0833333333333	1,921
2019.3333333333333	1,921
2019.6666666666667	1,920
2020	1,921
2020.3333333333333	1,921
2020.6666666666667	1,918
2020.9166666666667	1,920
2021.25	1,921
2021.5833333333333	1,918
2021.9166666666667	1,920
2022.25	1,921
2022.5	1,920
2022.8333333333333	1,919
2023.1666666666667	1,920
2023.5	1,920
2023.8333333333333	1,920
2024.1666666666667	1,921
2024.4166666666667	1,921
2024.75	1,918
2025.0833333333333	1,920
2025.4166666666667	1,921
2025.75	1,917
2026	1,919
2026.3333333333333	1,921
2026.6666666666667	1,914

Rate and persistence

-2.14 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

Island Park 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	1938–2026
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 1938 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-7184.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), Island Park Reservoir reservoir records, accessed 2026-10-05, hydrionis.com/reservoirs/reservoir-usbr-7184/

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 Island Park 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

1,054 monthly observations 1938–2026 Mm³

Spatially aggregatedHigh confidenceSeptember 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 131168. 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.