Jamestown Reservoir — storage

Storage now, against this reservoir's own record

36.99 Mm³

Stored, August 2026

42nd

Percentile among 73 Augs on record

-19.8%

Against the Aug 1991–2020 average

-4.2%

Change over the 12 months to 2026-08

Storage in August 2026 was around the middle of the Aug record, ranked against 73 other Augs held for this reservoir.

Storage, 1953–2026

Monthly mean storage

875 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 875 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 875 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
July 1959	25.4
November 1959	22.8
March 1960	22.6
June 1960	35.5
October 1960	32.4
February 1961	31.7
May 1961	32.0
September 1961	28.5
January 1962	26.5
April 1962	28.4
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
March 1970	34.6
July 1970	35.3
November 1970	36.4
February 1971	36.9
June 1971	44.1
October 1971	37.8
January 1972	34.9
May 1972	47.8
September 1972	38.4
December 1972	34.3
April 1973	36.8
August 1973	31.9
November 1973	30.7
March 1974	31.6
July 1974	45.7
October 1974	35.9
February 1975	34.6
June 1975	61.1
September 1975	38.7
January 1976	34.5
May 1976	43.7
August 1976	40.0
December 1976	34.0
April 1977	34.6
July 1977	34.0
November 1977	32.9
March 1978	33.8
June 1978	44.3
October 1978	35.1
February 1979	34.1
May 1979	86.1
September 1979	43.4
December 1979	35.4
April 1980	37.3
August 1980	37.5
November 1980	35.8
March 1981	37.9
July 1981	44.4
October 1981	38.0
February 1982	35.2
June 1982	62.7
September 1982	38.9
January 1983	38.3
May 1983	76.7
August 1983	45.0
December 1983	36.3
April 1984	48.6
July 1984	45.0
November 1984	34.9
March 1985	35.6
June 1985	39.9
October 1985	35.8
February 1986	35.3
May 1986	49.4
September 1986	41.3
January 1987	36.6
April 1987	98.9
August 1987	49.2
December 1987	36.2
March 1988	37.6
July 1988	36.9
November 1988	30.7
February 1989	30.4
June 1989	31.1
October 1989	28.6
January 1990	27.7
May 1990	27.1
August 1990	25.6
December 1990	23.7
April 1991	23.4
July 1991	22.9
November 1991	20.3
March 1992	21.2
June 1992	20.0
October 1992	18.3
February 1993	17.9
May 1993	32.2
September 1993	83.7
January 1994	39.9
April 1994	86.3
August 1994	42.0
December 1994	38.0
March 1995	53.9
July 1995	45.8
November 1995	36.5
February 1996	37.1
June 1996	60.1
October 1996	36.3
January 1997	35.3
May 1997	131
September 1997	42.1
December 1997	33.3
April 1998	75.9
August 1998	39.0
November 1998	27.8
March 1999	31.0
July 1999	57.4
October 1999	28.0
February 2000	26.9
June 2000	40.4
September 2000	54.9
January 2001	27.2
April 2001	97.8
August 2001	40.1
December 2001	34.5
March 2002	38.7
July 2002	38.5
November 2002	33.9
February 2003	33.3
June 2003	39.9
October 2003	35.0
January 2004	34.3
May 2004	49.3
September 2004	34.7
December 2004	36.2
April 2005	40.6
August 2005	38.5
November 2005	33.4
March 2006	33.5
July 2006	37.5
October 2006	34.8
February 2007	34.4
June 2007	41.5
September 2007	35.9
January 2008	34.1
May 2008	36.0
August 2008	37.0
December 2008	35.6
April 2009	164
July 2009	57.6
November 2009	35.2
March 2010	46.5
June 2010	64.3
October 2010	33.4
January 2011	33.0
May 2011	209
September 2011	158
December 2011	31.5
April 2012	39.6
August 2012	36.0
November 2012	33.3
March 2013	33.8
July 2013	47.6
October 2013	34.2
February 2014	30.6
June 2014	38.5
September 2014	35.4
January 2015	33.6
May 2015	37.0
August 2015	36.3
December 2015	34.2
April 2016	37.1
July 2016	38.2
November 2016	33.8
March 2017	37.9
June 2017	37.2
October 2017	35.1
February 2018	34.0
May 2018	39.3
September 2018	37.0
January 2019	34.3
April 2019	60.6
August 2019	37.1
December 2019	91.9
March 2020	25.3
July 2020	38.2
November 2020	34.5
February 2021	34.2
June 2021	33.6
September 2021	25.7
January 2022	26.1
May 2022	97.3
August 2022	38.3
December 2022	34.9
April 2023	43.5
July 2023	41.6
November 2023	33.5
March 2024	37.7
June 2024	42.9
October 2024	34.1
February 2025	32.8
May 2025	38.0
September 2025	35.0
January 2026	33.7
April 2026	43.2
August 2026	37.0

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	37.0
Sep	41.8	35.0
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

875 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 875 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 875 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
1959.5	434
1959.8333333333333	434
1960.1666666666667	434
1960.4166666666667	436
1960.75	435
1961.0833333333333	435
1961.3333333333333	435
1961.6666666666667	435
1962	434
1962.25	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
1970.1666666666667	436
1970.5	436
1970.8333333333333	436
1971.0833333333333	436
1971.4166666666667	437
1971.75	436
1972	436
1972.3333333333333	437
1972.6666666666667	436
1972.9166666666667	436
1973.25	436
1973.5833333333333	435
1973.8333333333333	435
1974.1666666666667	435
1974.5	437
1974.75	436
1975.0833333333333	436
1975.4166666666667	438
1975.6666666666667	436
1976	436
1976.3333333333333	437
1976.5833333333333	436
1976.9166666666667	436
1977.25	436
1977.5	436
1977.8333333333333	435
1978.1666666666667	436
1978.4166666666667	437
1978.75	436
1979.0833333333333	436
1979.3333333333333	439
1979.6666666666667	437
1979.9166666666667	436
1980.25	436
1980.5833333333333	436
1980.8333333333333	436
1981.1666666666667	436
1981.5	437
1981.75	436
1982.0833333333333	436
1982.4166666666667	438
1982.6666666666667	436
1983	436
1983.3333333333333	439
1983.5833333333333	437
1983.9166666666667	436
1984.25	437
1984.5	437
1984.8333333333333	436
1985.1666666666667	436
1985.4166666666667	436
1985.75	436
1986.0833333333333	436
1986.3333333333333	437
1986.6666666666667	436
1987	436
1987.25	439
1987.5833333333333	437
1987.9166666666667	436
1988.1666666666667	436
1988.5	436
1988.8333333333333	435
1989.0833333333333	435
1989.4166666666667	435
1989.75	435
1990	435
1990.3333333333333	435
1990.5833333333333	434
1990.9166666666667	434
1991.25	434
1991.5	434
1991.8333333333333	434
1992.1666666666667	434
1992.4166666666667	434
1992.75	433
1993.0833333333333	433
1993.3333333333333	435
1993.6666666666667	439
1994	436
1994.25	439
1994.5833333333333	437
1994.9166666666667	436
1995.1666666666667	437
1995.5	437
1995.8333333333333	436
1996.0833333333333	436
1996.4166666666667	438
1996.75	436
1997	436
1997.3333333333333	440
1997.6666666666667	436
1997.9166666666667	436
1998.25	439
1998.5833333333333	436
1998.8333333333333	435
1999.1666666666667	435
1999.5	438
1999.75	435
2000.0833333333333	435
2000.4166666666667	436
2000.6666666666667	438
2001	435
2001.25	439
2001.5833333333333	436
2001.9166666666667	436
2002.1666666666667	436
2002.5	436
2002.8333333333333	436
2003.0833333333333	436
2003.4166666666667	436
2003.75	436
2004	436
2004.3333333333333	437
2004.6666666666667	436
2004.9166666666667	436
2005.25	436
2005.5833333333333	436
2005.8333333333333	436
2006.1666666666667	436
2006.5	436
2006.75	436
2007.0833333333333	436
2007.4166666666667	436
2007.6666666666667	436
2008	436
2008.3333333333333	436
2008.5833333333333	436
2008.9166666666667	436
2009.25	441
2009.5	438
2009.8333333333333	436
2010.1666666666667	437
2010.4166666666667	438
2010.75	436
2011	435
2011.3333333333333	442
2011.6666666666667	441
2011.9166666666667	435
2012.25	436
2012.5833333333333	436
2012.8333333333333	436
2013.1666666666667	436
2013.5	437
2013.75	436
2014.0833333333333	435
2014.4166666666667	436
2014.6666666666667	436
2015	436
2015.3333333333333	436
2015.5833333333333	436
2015.9166666666667	436
2016.25	436
2016.5	436
2016.8333333333333	436
2017.1666666666667	436
2017.4166666666667	436
2017.75	436
2018.0833333333333	436
2018.3333333333333	436
2018.6666666666667	436
2019	436
2019.25	438
2019.5833333333333	436
2019.9166666666667	439
2020.1666666666667	435
2020.5	436
2020.8333333333333	436
2021.0833333333333	436
2021.4166666666667	436
2021.6666666666667	435
2022	435
2022.3333333333333	439
2022.5833333333333	436
2022.9166666666667	436
2023.25	437
2023.5	437
2023.8333333333333	436
2024.1666666666667	436
2024.4166666666667	437
2024.75	436
2025.0833333333333	436
2025.3333333333333	436
2025.6666666666667	436
2026	436
2026.25	437
2026.5833333333333	436

Rate and persistence

-0.14 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	98.5% 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	99% of the months between 1953 and 2026 are held. Monthly means of the publisher's own daily record.
Last read from the publisher	2026-09-01
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-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 2026-09-02, 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

875 monthly observations 1953–2026 Mm³

Spatially aggregatedHigh confidenceAugust 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 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.