Jamestown Reservoir — storage

Storage now, against this reservoir's own record

34.67 Mm³

Stored, September 2026

35th

Percentile among 73 Seps on record

-17.0%

Against the Sep 1991–2020 average

-0.8%

Change over the 12 months to 2026-09

Storage in September 2026 was around the middle of the Sep record, ranked against 73 other Seps held for this reservoir.

Storage, 1953–2026

Monthly mean storage

876 monthly values, 1953 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 876 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 876 would be longer than this page and unusable with a screen reader.
Period	Jamestown Reservoir (Mm³)
October 1953	0
February 1954	1.26
May 1954	1.55
September 1954	4.96
January 1955	4.24
April 1955	6.41
August 1955	11.2
December 1955	9.57
March 1956	9.93
July 1956	20.2
November 1956	18.7
February 1957	18.1
June 1957	18.2
October 1957	18.7
January 1958	22.7
May 1958	32.4
September 1958	29.5
December 1958	27.6
April 1959	26.2
August 1959	24.2
November 1959	22.8
March 1960	22.6
July 1960	36.0
October 1960	32.4
February 1961	31.7
June 1961	30.8
September 1961	28.5
January 1962	26.5
May 1962	28.7
August 1962	33.8
December 1962	32.0
March 1963	31.4
July 1963	30.7
November 1963	27.2
February 1964	26.6
June 1964	28.4
October 1964	24.3
January 1965	22.1
May 1965	41.5
September 1965	34.3
December 1965	39.7
April 1966	82.2
August 1966	42.3
November 1966	35.6
March 1967	37.0
July 1967	42.5
October 1967	35.2
February 1968	34.4
June 1968	36.9
September 1968	34.3
January 1969	35.2
May 1969	119
August 1969	46.4
December 1969	34.6
April 1970	35.9
July 1970	35.3
November 1970	36.4
March 1971	37.5
June 1971	44.1
October 1971	37.8
February 1972	34.8
May 1972	47.8
September 1972	38.4
January 1973	34.3
April 1973	36.8
August 1973	31.9
December 1973	30.6
March 1974	31.6
July 1974	45.7
November 1974	35.3
February 1975	34.6
June 1975	61.1
October 1975	35.2
January 1976	34.5
May 1976	43.7
September 1976	36.9
December 1976	34.0
April 1977	34.6
August 1977	33.1
November 1977	32.9
March 1978	33.8
July 1978	44.2
October 1978	35.1
February 1979	34.1
June 1979	72.3
September 1979	43.4
January 1980	35.2
May 1980	36.7
August 1980	37.5
December 1980	35.2
March 1981	37.9
July 1981	44.4
November 1981	36.3
February 1982	35.2
June 1982	62.7
October 1982	37.1
January 1983	38.3
May 1983	76.7
September 1983	40.0
December 1983	36.3
April 1984	48.6
August 1984	41.0
November 1984	34.9
March 1985	35.6
July 1985	39.3
October 1985	35.8
February 1986	35.3
June 1986	45.8
September 1986	41.3
January 1987	36.6
May 1987	87.0
August 1987	49.2
December 1987	36.2
April 1988	39.5
July 1988	36.9
November 1988	30.7
March 1989	30.8
June 1989	31.1
October 1989	28.6
February 1990	27.6
May 1990	27.1
September 1990	24.9
January 1991	23.5
April 1991	23.4
August 1991	21.7
December 1991	20.2
March 1992	21.2
July 1992	19.7
November 1992	18.2
February 1993	17.9
June 1993	39.0
October 1993	50.7
January 1994	39.9
May 1994	62.7
September 1994	40.9
December 1994	38.0
April 1995	113
August 1995	37.5
November 1995	36.5
March 1996	44.8
July 1996	56.4
October 1996	36.3
February 1997	34.3
June 1997	86.2
September 1997	42.1
January 1998	33.9
May 1998	64.5
August 1998	39.0
December 1998	28.1
April 1999	87.1
July 1999	57.4
November 1999	27.5
February 2000	26.9
June 2000	40.4
October 2000	36.1
January 2001	27.2
May 2001	82.0
September 2001	35.6
December 2001	34.5
April 2002	40.7
August 2002	38.2
November 2002	33.9
March 2003	33.9
July 2003	38.4
October 2003	35.0
February 2004	34.4
June 2004	40.9
September 2004	34.7
January 2005	36.3
May 2005	40.8
August 2005	38.5
December 2005	32.5
April 2006	35.9
July 2006	37.5
November 2006	34.6
March 2007	36.7
June 2007	41.5
October 2007	36.0
February 2008	34.1
May 2008	36.0
September 2008	36.3
January 2009	36.0
April 2009	164
August 2009	39.3
December 2009	34.2
March 2010	46.5
July 2010	42.0
November 2010	33.3
February 2011	32.3
June 2011	139
October 2011	65.8
January 2012	32.2
May 2012	38.7
September 2012	34.9
December 2012	33.5
April 2013	34.8
August 2013	36.9
November 2013	32.9
March 2014	31.7
July 2014	38.0
October 2014	33.4
February 2015	33.6
June 2015	37.8
September 2015	36.1
January 2016	34.0
May 2016	37.6
August 2016	39.0
December 2016	33.5
April 2017	68.8
July 2017	38.4
November 2017	34.0
February 2018	34.0
June 2018	37.3
October 2018	34.5
January 2019	34.3
May 2019	54.8
September 2019	36.7
December 2019	91.9
April 2020	71.6
August 2020	36.9
November 2020	34.5
March 2021	34.6
July 2021	30.5
October 2021	25.7
February 2022	26.4
June 2022	102
September 2022	34.1
January 2023	35.9
May 2023	113
August 2023	36.0
December 2023	34.0
April 2024	38.6
July 2024	45.3
November 2024	34.2
March 2025	33.9
June 2025	37.5
October 2025	34.0
February 2026	34.5
May 2026	37.7
September 2026	34.7

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	33.6	33.7
Feb	32.9	34.5
Mar	35.0	38.1
Apr	63.0	43.2
May	67.4	37.7
Jun	51.9	37.2
Jul	45.0	38.8
Aug	46.1	36.9
Sep	41.8	34.7
Oct	35.7	34.0
Nov	35.2	35.5
Dec	34.6	33.9

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

876 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 876 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 876 would be longer than this page and unusable with a screen reader.
Period	Jamestown Reservoir (m)
1953.75	0
1954.0833333333333	427
1954.3333333333333	427
1954.6666666666667	429
1955	429
1955.25	430
1955.5833333333333	432
1955.9166666666667	431
1956.1666666666667	431
1956.5	433
1956.8333333333333	433
1957.0833333333333	433
1957.4166666666667	433
1957.75	433
1958	434
1958.3333333333333	435
1958.6666666666667	435
1958.9166666666667	435
1959.25	434
1959.5833333333333	434
1959.8333333333333	434
1960.1666666666667	434
1960.5	436
1960.75	435
1961.0833333333333	435
1961.4166666666667	435
1961.6666666666667	435
1962	434
1962.3333333333333	435
1962.5833333333333	435
1962.9166666666667	435
1963.1666666666667	435
1963.5	435
1963.8333333333333	435
1964.0833333333333	434
1964.4166666666667	435
1964.75	434
1965	434
1965.3333333333333	437
1965.6666666666667	436
1965.9166666666667	436
1966.25	439
1966.5833333333333	437
1966.8333333333333	436
1967.1666666666667	436
1967.5	437
1967.75	436
1968.0833333333333	436
1968.4166666666667	436
1968.6666666666667	436
1969	436
1969.3333333333333	440
1969.5833333333333	437
1969.9166666666667	436
1970.25	436
1970.5	436
1970.8333333333333	436
1971.1666666666667	436
1971.4166666666667	437
1971.75	436
1972.0833333333333	436
1972.3333333333333	437
1972.6666666666667	436
1973	436
1973.25	436
1973.5833333333333	435
1973.9166666666667	435
1974.1666666666667	435
1974.5	437
1974.8333333333333	436
1975.0833333333333	436
1975.4166666666667	438
1975.75	436
1976	436
1976.3333333333333	437
1976.6666666666667	436
1976.9166666666667	436
1977.25	436
1977.5833333333333	435
1977.8333333333333	435
1978.1666666666667	436
1978.5	437
1978.75	436
1979.0833333333333	436
1979.4166666666667	438
1979.6666666666667	437
1980	436
1980.3333333333333	436
1980.5833333333333	436
1980.9166666666667	436
1981.1666666666667	436
1981.5	437
1981.8333333333333	436
1982.0833333333333	436
1982.4166666666667	438
1982.75	436
1983	436
1983.3333333333333	439
1983.6666666666667	436
1983.9166666666667	436
1984.25	437
1984.5833333333333	436
1984.8333333333333	436
1985.1666666666667	436
1985.5	436
1985.75	436
1986.0833333333333	436
1986.4166666666667	437
1986.6666666666667	436
1987	436
1987.3333333333333	439
1987.5833333333333	437
1987.9166666666667	436
1988.25	436
1988.5	436
1988.8333333333333	435
1989.1666666666667	435
1989.4166666666667	435
1989.75	435
1990.0833333333333	435
1990.3333333333333	435
1990.6666666666667	434
1991	434
1991.25	434
1991.5833333333333	434
1991.9166666666667	434
1992.1666666666667	434
1992.5	433
1992.8333333333333	433
1993.0833333333333	433
1993.4166666666667	436
1993.75	437
1994	436
1994.3333333333333	438
1994.6666666666667	436
1994.9166666666667	436
1995.25	440
1995.5833333333333	436
1995.8333333333333	436
1996.1666666666667	437
1996.5	438
1996.75	436
1997.0833333333333	436
1997.4166666666667	439
1997.6666666666667	436
1998	436
1998.3333333333333	438
1998.5833333333333	436
1998.9166666666667	435
1999.25	439
1999.5	438
1999.8333333333333	435
2000.0833333333333	435
2000.4166666666667	436
2000.75	436
2001	435
2001.3333333333333	439
2001.6666666666667	436
2001.9166666666667	436
2002.25	436
2002.5833333333333	436
2002.8333333333333	436
2003.1666666666667	436
2003.5	436
2003.75	436
2004.0833333333333	436
2004.4166666666667	436
2004.6666666666667	436
2005	436
2005.3333333333333	436
2005.5833333333333	436
2005.9166666666667	435
2006.25	436
2006.5	436
2006.8333333333333	436
2007.1666666666667	436
2007.4166666666667	436
2007.75	436
2008.0833333333333	436
2008.3333333333333	436
2008.6666666666667	436
2009	436
2009.25	441
2009.5833333333333	436
2009.9166666666667	436
2010.1666666666667	437
2010.5	436
2010.8333333333333	436
2011.0833333333333	435
2011.4166666666667	440
2011.75	438
2012	435
2012.3333333333333	436
2012.6666666666667	436
2012.9166666666667	436
2013.25	436
2013.5833333333333	436
2013.8333333333333	436
2014.1666666666667	435
2014.5	436
2014.75	436
2015.0833333333333	436
2015.4166666666667	436
2015.6666666666667	436
2016	436
2016.3333333333333	436
2016.5833333333333	436
2016.9166666666667	436
2017.25	438
2017.5	436
2017.8333333333333	436
2018.0833333333333	436
2018.4166666666667	436
2018.75	436
2019	436
2019.3333333333333	438
2019.6666666666667	436
2019.9166666666667	439
2020.25	438
2020.5833333333333	436
2020.8333333333333	436
2021.1666666666667	436
2021.5	435
2021.75	435
2022.0833333333333	435
2022.4166666666667	439
2022.6666666666667	436
2023	436
2023.3333333333333	440
2023.5833333333333	436
2023.9166666666667	436
2024.25	436
2024.5	437
2024.8333333333333	436
2025.1666666666667	436
2025.4166666666667	436
2025.75	436
2026.0833333333333	436
2026.3333333333333	436
2026.6666666666667	436

Rate and persistence

-0.02 Mm³

Mean drawdown per month over 12 months

0 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

Jamestown 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	1953–2026
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 1953 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-379.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), Jamestown Reservoir reservoir records, accessed 2026-10-05, hydrionis.com/reservoirs/reservoir-usbr-379/

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 Jamestown 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

876 monthly observations 1953–2026 Mm³

Spatially aggregatedHigh confidenceSeptember 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 450. 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.