Nelson Reservoir — storage

Storage now, against this reservoir's own record

65.95 Mm³

Stored, August 2026

42nd

Percentile among 44 Augs on record

-3.6%

Against the Aug 1991–2020 average

-12.1%

Change over the 12 months to 2026-08

Storage in August 2026 was around the middle of the Aug record, ranked against 44 other Augs held for this reservoir.

Storage, 1980–2026

Monthly mean storage

520 monthly values, 1980 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 520 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 520 would be longer than this page and unusable with a screen reader.
Period	Nelson Reservoir (Mm³)
October 1980	51.4
December 1980	51.2
February 1981	48.4
May 1981	61.5
July 1981	52.7
September 1981	42.8
November 1981	62.1
January 1982	58.5
March 1982	59.2
June 1982	91.5
August 1982	78.9
October 1982	85.1
December 1982	84.1
February 1983	78.8
April 1983	78.4
July 1983	58.6
September 1983	47.6
November 1983	50.1
January 1984	47.4
March 1984	46.4
May 1984	43.6
August 1984	25.5
October 1984	38.5
December 1984	39.6
February 1985	37.6
April 1985	45.9
June 1985	40.5
September 1985	34.4
November 1985	63.5
January 1986	59.7
March 1986	73.4
May 1986	97.0
July 1986	83.6
October 1986	88.1
December 1986	82.9
February 1987	77.6
April 1987	81.8
June 1987	85.4
September 1987	82.2
November 1987	81.9
January 1988	79.1
March 1988	73.8
May 1988	64.7
July 1988	38.5
October 1988	29.4
December 1988	27.8
February 1989	26.3
April 1989	41.4
June 1989	64.1
August 1989	54.8
November 1989	74.8
January 1990	70.1
March 1990	68.0
May 1990	90.1
July 1990	78.6
September 1990	76.3
December 1990	71.2
February 1991	67.8
April 1991	67.0
June 1991	67.1
August 1991	71.8
May 1994	94.0
August 1994	66.0
October 1994	54.4
December 1994	50.5
February 1995	48.2
April 1995	58.0
June 1995	62.9
September 1995	71.8
November 1995	61.0
January 1996	57.8
March 1996	59.7
May 1996	92.8
August 1996	73.2
October 1996	70.4
December 1996	65.6
February 1997	62.0
April 1997	74.6
June 1997	83.0
September 1997	75.0
November 1997	92.2
January 1998	85.7
March 1998	80.6
May 1998	68.2
July 1998	65.8
October 1998	69.9
December 1998	70.3
February 1999	66.8
April 1999	76.2
June 1999	90.6
August 1999	70.5
November 1999	77.5
January 2000	71.3
March 2000	68.6
May 2000	62.1
July 2000	57.7
September 2000	33.4
December 2000	39.4
February 2001	37.8
April 2001	43.4
June 2001	37.0
August 2001	45.8
October 2001	40.1
January 2002	38.2
March 2002	36.6
May 2002	46.6
July 2002	51.0
September 2002	60.7
December 2002	78.4
February 2003	73.4
April 2003	86.7
June 2003	82.0
August 2003	58.3
October 2003	61.8
January 2004	55.3
March 2004	54.1
May 2004	70.5
July 2004	75.5
September 2004	69.1
November 2004	77.3
February 2005	69.6
April 2005	73.1
June 2005	67.9
August 2005	59.3
October 2005	72.1
December 2005	68.7
March 2006	64.1
May 2006	88.3
July 2006	74.8
September 2006	53.9
November 2006	60.1
January 2007	56.4
April 2007	78.3
June 2007	96.3
August 2007	67.7
October 2007	67.9
December 2007	64.1
March 2008	59.1
May 2008	58.9
July 2008	70.2
September 2008	72.7
November 2008	77.0
January 2009	72.4
April 2009	85.3
June 2009	85.8
August 2009	79.5
October 2009	87.2
December 2009	81.4
February 2010	76.6
May 2010	95.9
July 2010	93.6
September 2010	94.9
November 2010	89.2
January 2011	85.4
March 2011	81.5
June 2011	91.2
August 2011	87.6
October 2011	92.5
December 2011	89.3
February 2012	84.6
April 2012	83.1
July 2012	88.2
September 2012	77.2
November 2012	80.6
January 2013	76.9
March 2013	77.3
May 2013	94.2
August 2013	94.3
October 2013	92.9
December 2013	89.0
February 2014	85.0
April 2014	90.9
July 2014	92.8
September 2014	88.6
November 2014	84.0
January 2015	79.7
March 2015	78.3
May 2015	95.4
August 2015	70.5
October 2015	81.0
December 2015	76.1
February 2016	72.7
April 2016	77.9
June 2016	92.6
September 2016	32.6
November 2016	35.8
January 2017	34.6
March 2017	41.8
May 2017	90.0
July 2017	65.5
October 2017	62.7
December 2017	59.7
February 2018	56.4
April 2018	65.1
June 2018	88.3
August 2018	80.0
November 2018	88.3
January 2019	82.8
March 2019	81.1
May 2019	95.6
July 2019	95.3
September 2019	95.6
December 2019	87.1
February 2020	83.1
April 2020	94.7
June 2020	86.6
August 2020	73.4
November 2020	66.0
January 2021	62.4
March 2021	64.2
May 2021	73.2
July 2021	47.5
September 2021	53.8
December 2021	54.9
February 2022	52.1
April 2022	54.0
June 2022	50.0
August 2022	46.6
October 2022	56.3
January 2023	52.4
March 2023	50.0
May 2023	80.4
July 2023	89.9
September 2023	76.5
November 2023	79.5
February 2024	72.9
April 2024	92.1
June 2024	82.6
August 2024	78.7
October 2024	74.4
December 2024	69.0
March 2025	76.9
May 2025	81.7
July 2025	66.7
September 2025	77.6
November 2025	70.5
January 2026	67.3
April 2026	70.6
June 2026	52.8
August 2026	66.0

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	67.8	67.3
Feb	66.2	66.0
Mar	66.4	65.9
Apr	76.0	70.6
May	82.9	66.0
Jun	79.2	52.8
Jul	78.1	70.7
Aug	68.4	66.0
Sep	70.3	77.6
Oct	72.6	73.4
Nov	71.8	70.5
Dec	69.6	69.0

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

563 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 563 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 563 would be longer than this page and unusable with a screen reader.
Period	Nelson Reservoir (m)
1979.75	676
1979.9166666666667	676
1980.1666666666667	676
1980.3333333333333	675
1980.5	674
1980.75	674
1980.9166666666667	674
1981.0833333333333	674
1981.3333333333333	675
1981.5	674
1981.75	674
1981.9166666666667	675
1982.0833333333333	675
1982.3333333333333	677
1982.5	677
1982.6666666666667	676
1982.9166666666667	676
1983.0833333333333	676
1983.25	676
1983.5	675
1983.6666666666667	674
1983.8333333333333	674
1984.0833333333333	674
1984.25	674
1984.4166666666667	672
1984.6666666666667	671
1984.8333333333333	673
1985	673
1985.25	673
1985.4166666666667	673
1985.6666666666667	672
1985.8333333333333	675
1986	675
1986.25	677
1986.4166666666667	677
1986.5833333333333	676
1986.8333333333333	676
1987	676
1987.1666666666667	676
1987.4166666666667	676
1987.5833333333333	676
1987.75	676
1988	676
1988.1666666666667	676
1988.3333333333333	675
1988.5833333333333	672
1988.75	672
1989	671
1989.1666666666667	672
1989.3333333333333	674
1989.5833333333333	674
1989.75	676
1989.9166666666667	676
1990.1666666666667	675
1990.3333333333333	677
1990.5	676
1990.75	676
1990.9166666666667	676
1991.0833333333333	675
1991.3333333333333	675
1991.5	676
1991.6666666666667	676
1991.9166666666667	676
1992.0833333333333	675
1992.25	675
1992.5	674
1992.6666666666667	673
1992.9166666666667	673
1993.0833333333333	673
1993.25	675
1993.5	676
1993.6666666666667	677
1993.8333333333333	677
1994.0833333333333	676
1994.25	677
1994.4166666666667	677
1994.6666666666667	675
1994.8333333333333	674
1995	674
1995.25	674
1995.4166666666667	675
1995.5833333333333	675
1995.8333333333333	675
1996	674
1996.25	676
1996.4166666666667	677
1996.5833333333333	676
1996.8333333333333	675
1997	675
1997.1666666666667	675
1997.4166666666667	676
1997.5833333333333	675
1997.75	676
1998	676
1998.1666666666667	676
1998.3333333333333	675
1998.5833333333333	675
1998.75	675
1998.9166666666667	675
1999.1666666666667	675
1999.3333333333333	676
1999.5	677
1999.75	676
1999.9166666666667	676
2000.1666666666667	675
2000.3333333333333	675
2000.5	674
2000.75	672
2000.9166666666667	673
2001.0833333333333	672
2001.3333333333333	674
2001.5	674
2001.6666666666667	673
2001.9166666666667	673
2002.0833333333333	673
2002.25	673
2002.5	674
2002.6666666666667	675
2002.8333333333333	676
2003.0833333333333	676
2003.25	677
2003.5	676
2003.6666666666667	675
2003.8333333333333	675
2004.0833333333333	674
2004.25	675
2004.4166666666667	676
2004.6666666666667	675
2004.8333333333333	676
2005	676
2005.25	676
2005.4166666666667	675
2005.5833333333333	675
2005.8333333333333	676
2006	675
2006.1666666666667	675
2006.4166666666667	676
2006.5833333333333	674
2006.8333333333333	675
2007	674
2007.1666666666667	675
2007.4166666666667	677
2007.5833333333333	675
2007.75	675
2008	675
2008.1666666666667	675
2008.3333333333333	675
2008.5833333333333	675
2008.75	676
2008.9166666666667	676
2009.1666666666667	675
2009.3333333333333	677
2009.5	676
2009.75	677
2009.9166666666667	676
2010.0833333333333	676
2010.3333333333333	677
2010.5	677
2010.75	677
2010.9166666666667	677
2011.0833333333333	676
2011.3333333333333	677
2011.5	677
2011.6666666666667	677
2011.9166666666667	677
2012.0833333333333	676
2012.25	676
2012.5	677
2012.6666666666667	676
2012.8333333333333	676
2013.0833333333333	676
2013.25	677
2013.4166666666667	677
2013.6666666666667	677
2013.8333333333333	677
2014.0833333333333	676
2014.25	677
2014.4166666666667	677
2014.6666666666667	677
2014.8333333333333	676
2015	676
2015.25	677
2015.4166666666667	677
2015.5833333333333	675
2015.8333333333333	676
2016	676
2016.1666666666667	676
2016.4166666666667	677
2016.5833333333333	673
2016.75	672
2017	672
2017.1666666666667	673
2017.3333333333333	677
2017.5833333333333	674
2017.75	675
2018	675
2018.1666666666667	674
2018.3333333333333	677
2018.5833333333333	676
2018.75	677
2018.9166666666667	676
2019.1666666666667	676
2019.3333333333333	677
2019.5	677
2019.75	677
2019.9166666666667	677
2020.0833333333333	676
2020.3333333333333	677
2020.5	677
2020.6666666666667	676
2020.9166666666667	675
2021.0833333333333	675
2021.3333333333333	676
2021.5	674
2021.6666666666667	674
2021.9166666666667	674
2022.0833333333333	674
2022.25	674
2022.5	675
2022.6666666666667	674
2022.8333333333333	674
2023.0833333333333	674
2023.25	675
2023.4166666666667	677
2023.6666666666667	676
2023.8333333333333	676
2024	676
2024.25	677
2024.4166666666667	676
2024.5833333333333	676
2024.8333333333333	676
2025	675
2025.25	677
2025.4166666666667	675
2025.5833333333333	676
2025.8333333333333	675
2026	675
2026.1666666666667	675
2026.4166666666667	674
2026.5833333333333	675

Rate and persistence

-0.76 Mm³

Mean drawdown per month over 12 months

1 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

Nelson 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	1980–2026
Completeness	92.2% 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	92% of the months between 1980 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-424.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), Nelson Reservoir reservoir records, accessed 2026-09-02, hydrionis.com/reservoirs/reservoir-usbr-424/

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 Nelson 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

520 monthly observations 1980–2026 Mm³

Spatially aggregatedHigh confidenceAugust 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 618. 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.