Shadow Mountain Lake — storage

Storage now, against this reservoir's own record

20.88 Mm³

Stored, September 2026

8th

Percentile among 66 Seps on record

-4.7%

Against the Sep 1991–2020 average

+1.2%

Change over the 12 months to 2026-09

Storage in September 2026 was lower than almost every other Sep on record, ranked against 66 other Seps held for this reservoir.

Storage, 1953–2026

Monthly mean storage

793 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 793 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 793 would be longer than this page and unusable with a screen reader.
Period	Shadow Mountain Lake (Mm³)
October 1953	22.2
January 1954	22.3
May 1954	21.9
August 1954	21.7
November 1954	21.7
March 1955	22.1
June 1955	22.1
September 1955	21.9
January 1956	22.3
April 1956	22.0
July 1956	22.1
October 1956	22.0
February 1957	22.2
May 1957	21.5
August 1957	22.2
December 1957	21.8
March 1958	21.8
June 1958	21.3
October 1958	21.8
January 1959	21.8
April 1959	21.8
August 1959	21.8
November 1959	21.9
February 1960	21.7
June 1960	21.5
September 1960	21.7
December 1960	22.0
March 1961	21.9
July 1961	21.7
October 1961	22.2
January 1962	21.9
May 1962	21.8
August 1962	21.7
November 1962	22.0
March 1963	21.9
June 1963	22.1
September 1963	21.8
January 1964	21.9
April 1964	21.8
July 1964	21.9
November 1964	21.7
February 1965	21.8
May 1965	21.6
August 1965	22.0
December 1965	21.9
March 1966	21.8
June 1966	22.1
October 1966	21.8
January 1967	21.9
April 1967	22.1
August 1967	21.9
November 1967	21.7
February 1968	21.8
June 1968	21.2
September 1968	21.7
December 1968	21.7
April 1969	21.8
July 1969	21.9
October 1969	21.7
February 1970	21.8
May 1970	21.4
August 1970	21.9
November 1970	21.8
March 1971	21.8
June 1971	21.2
September 1971	21.8
January 1972	22.0
April 1972	21.9
July 1972	21.9
November 1972	21.8
February 1973	21.9
May 1973	21.8
September 1973	21.9
December 1973	21.8
March 1974	21.9
July 1974	21.8
October 1974	21.9
January 1975	21.9
April 1975	21.9
August 1975	21.8
November 1975	22.0
February 1976	21.9
June 1976	21.7
September 1976	21.9
December 1976	21.9
April 1977	22.0
July 1977	21.9
October 1977	22.1
February 1978	22.0
May 1978	21.7
August 1978	21.8
December 1978	22.0
March 1979	21.9
June 1979	21.1
September 1979	21.9
January 1980	21.9
April 1980	21.9
July 1980	22.0
June 1986	20.9
September 1986	22.0
December 1986	22.0
October 1987	22.0
January 1988	21.9
September 1988	22.1
January 1989	21.9
April 1989	21.9
July 1989	22.1
November 1989	22.2
February 1990	22.1
May 1990	21.7
September 1990	26.5
December 1990	22.1
March 1991	22.0
June 1991	21.5
October 1991	18.1
January 1992	22.0
April 1992	21.9
August 1992	21.9
November 1992	21.8
February 1993	22.0
June 1993	21.2
September 1993	22.0
December 1993	21.9
April 1994	21.9
July 1994	22.0
October 1994	22.1
February 1995	22.1
May 1995	21.8
August 1995	22.0
November 1995	22.1
March 1996	22.0
June 1996	21.6
September 1996	22.1
January 1997	22.1
April 1997	22.0
July 1997	22.1
November 1997	22.0
February 1998	22.0
May 1998	21.6
September 1998	21.9
December 1998	21.9
March 1999	22.0
July 1999	21.8
October 1999	21.7
January 2000	22.0
May 2000	21.6
August 2000	21.9
November 2000	21.8
February 2001	22.0
July 2001	21.8
December 2001	22.0
March 2002	22.0
July 2002	21.7
October 2002	21.8
January 2003	22.1
May 2003	21.5
August 2003	22.0
November 2003	22.0
March 2004	22.0
June 2004	21.9
September 2004	21.9
January 2005	22.0
April 2005	22.0
July 2005	21.9
October 2005	22.0
February 2006	22.0
May 2006	21.6
August 2006	22.0
January 2007	22.0
April 2007	21.8
July 2007	22.0
November 2007	22.0
February 2008	21.9
May 2008	21.8
September 2008	22.1
December 2008	22.0
March 2009	22.0
July 2009	21.8
November 2009	21.9
February 2010	22.0
May 2010	21.8
September 2010	21.7
December 2010	22.0
March 2011	22.0
July 2011	21.1
October 2011	22.0
January 2012	21.9
May 2012	21.9
August 2012	22.0
November 2012	21.8
March 2013	22.0
June 2013	21.4
September 2013	21.9
January 2014	22.1
April 2014	22.0
July 2014	21.7
November 2014	22.0
February 2015	22.0
May 2015	21.6
August 2015	21.8
December 2015	22.0
March 2016	22.0
June 2016	21.3
October 2016	22.0
January 2017	22.0
April 2017	21.7
August 2017	21.7
November 2017	21.9
February 2018	22.0
June 2018	21.4
September 2018	21.8
December 2018	22.0
April 2019	22.0
July 2019	21.5
October 2019	21.8
January 2020	21.9
May 2020	21.4
August 2020	21.8
November 2020	21.8
March 2021	22.0
June 2021	20.6
September 2021	20.8
January 2022	20.9
April 2022	20.9
July 2022	20.6
November 2022	20.7
February 2023	21.0
May 2023	20.7
September 2023	20.9
December 2023	20.9
March 2024	20.9
June 2024	20.6
October 2024	20.9
January 2025	21.0
April 2025	20.9
August 2025	20.7
November 2025	20.8
February 2026	21.0
June 2026	20.8
September 2026	20.9

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	22.0	21.0
Feb	22.0	21.0
Mar	22.0	20.9
Apr	21.9	20.8
May	21.7	20.9
Jun	21.5	20.8
Jul	21.8	20.7
Aug	21.9	20.7
Sep	21.9	20.9
Oct	21.7	20.6
Nov	21.7	20.8
Dec	21.9	21.0

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

793 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 793 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 793 would be longer than this page and unusable with a screen reader.
Period	Shadow Mountain Lake (m)
1953.75	2,550
1954	2,550
1954.3333333333333	2,550
1954.5833333333333	2,550
1954.8333333333333	2,550
1955.1666666666667	2,550
1955.4166666666667	2,550
1955.6666666666667	2,550
1956	2,550
1956.25	2,550
1956.5	2,550
1956.75	2,550
1957.0833333333333	2,550
1957.3333333333333	2,550
1957.5833333333333	2,550
1957.9166666666667	2,550
1958.1666666666667	2,550
1958.4166666666667	2,550
1958.75	2,550
1959	2,550
1959.25	2,550
1959.5833333333333	2,550
1959.8333333333333	2,550
1960.0833333333333	2,550
1960.4166666666667	2,550
1960.6666666666667	2,550
1960.9166666666667	2,550
1961.1666666666667	2,550
1961.5	2,550
1961.75	2,550
1962	2,550
1962.3333333333333	2,550
1962.5833333333333	2,550
1962.8333333333333	2,550
1963.1666666666667	2,550
1963.4166666666667	2,550
1963.6666666666667	2,550
1964	2,550
1964.25	2,550
1964.5	2,550
1964.8333333333333	2,550
1965.0833333333333	2,550
1965.3333333333333	2,550
1965.5833333333333	2,550
1965.9166666666667	2,550
1966.1666666666667	2,550
1966.4166666666667	2,550
1966.75	2,550
1967	2,550
1967.25	2,550
1967.5833333333333	2,550
1967.8333333333333	2,550
1968.0833333333333	2,550
1968.4166666666667	2,550
1968.6666666666667	2,550
1968.9166666666667	2,550
1969.25	2,550
1969.5	2,550
1969.75	2,550
1970.0833333333333	2,550
1970.3333333333333	2,550
1970.5833333333333	2,550
1970.8333333333333	2,550
1971.1666666666667	2,550
1971.4166666666667	2,550
1971.6666666666667	2,550
1972	2,550
1972.25	2,550
1972.5	2,550
1972.8333333333333	2,550
1973.0833333333333	2,550
1973.3333333333333	2,550
1973.6666666666667	2,550
1973.9166666666667	2,550
1974.1666666666667	2,550
1974.5	2,550
1974.75	2,550
1975	2,550
1975.25	2,550
1975.5833333333333	2,550
1975.8333333333333	2,550
1976.0833333333333	2,550
1976.4166666666667	2,550
1976.6666666666667	2,550
1976.9166666666667	2,550
1977.25	2,550
1977.5	2,550
1977.75	2,550
1978.0833333333333	2,550
1978.3333333333333	2,550
1978.5833333333333	2,550
1978.9166666666667	2,550
1979.1666666666667	2,550
1979.4166666666667	2,550
1979.6666666666667	2,550
1980	2,550
1980.25	2,550
1980.5	2,550
1986.4166666666667	2,550
1986.6666666666667	2,550
1986.9166666666667	2,550
1987.75	2,550
1988	2,550
1988.6666666666667	2,550
1989	2,550
1989.25	2,550
1989.5	2,550
1989.8333333333333	2,550
1990.0833333333333	2,550
1990.3333333333333	2,550
1990.6666666666667	2,551
1990.9166666666667	2,550
1991.1666666666667	2,550
1991.4166666666667	2,550
1991.75	2,550
1992	2,550
1992.25	2,550
1992.5833333333333	2,550
1992.8333333333333	2,550
1993.0833333333333	2,550
1993.4166666666667	2,550
1993.6666666666667	2,550
1993.9166666666667	2,550
1994.25	2,550
1994.5	2,550
1994.75	2,550
1995.0833333333333	2,550
1995.3333333333333	2,550
1995.5833333333333	2,550
1995.8333333333333	2,550
1996.1666666666667	2,550
1996.4166666666667	2,550
1996.6666666666667	2,550
1997	2,550
1997.25	2,550
1997.5	2,550
1997.8333333333333	2,550
1998.0833333333333	2,550
1998.3333333333333	2,550
1998.6666666666667	2,550
1998.9166666666667	2,550
1999.1666666666667	2,550
1999.5	2,550
1999.75	2,550
2000	2,550
2000.3333333333333	2,550
2000.5833333333333	2,550
2000.8333333333333	2,550
2001.0833333333333	2,550
2001.5	2,550
2001.9166666666667	2,550
2002.1666666666667	2,550
2002.5	2,550
2002.75	2,550
2003	2,550
2003.3333333333333	2,550
2003.5833333333333	2,550
2003.8333333333333	2,550
2004.1666666666667	2,550
2004.4166666666667	2,550
2004.6666666666667	2,550
2005	2,550
2005.25	2,550
2005.5	2,550
2005.75	2,550
2006.0833333333333	2,550
2006.3333333333333	2,550
2006.5833333333333	2,550
2007	2,550
2007.25	2,550
2007.5	2,550
2007.8333333333333	2,550
2008.0833333333333	2,550
2008.3333333333333	2,550
2008.6666666666667	2,550
2008.9166666666667	2,550
2009.1666666666667	2,550
2009.5	2,550
2009.8333333333333	2,550
2010.0833333333333	2,550
2010.3333333333333	2,550
2010.6666666666667	2,550
2010.9166666666667	2,550
2011.1666666666667	2,550
2011.5	2,550
2011.75	2,550
2012	2,550
2012.3333333333333	2,550
2012.5833333333333	2,550
2012.8333333333333	2,550
2013.1666666666667	2,550
2013.4166666666667	2,550
2013.6666666666667	2,550
2014	2,550
2014.25	2,550
2014.5	2,550
2014.8333333333333	2,550
2015.0833333333333	2,550
2015.3333333333333	2,550
2015.5833333333333	2,550
2015.9166666666667	2,550
2016.1666666666667	2,550
2016.4166666666667	2,550
2016.75	2,550
2017	2,550
2017.25	2,550
2017.5833333333333	2,550
2017.8333333333333	2,550
2018.0833333333333	2,550
2018.4166666666667	2,550
2018.6666666666667	2,550
2018.9166666666667	2,550
2019.25	2,550
2019.5	2,550
2019.75	2,550
2020	2,550
2020.3333333333333	2,550
2020.5833333333333	2,550
2020.8333333333333	2,550
2021.1666666666667	2,550
2021.4166666666667	2,550
2021.6666666666667	2,550
2022	2,550
2022.25	2,550
2022.5	2,550
2022.8333333333333	2,550
2023.0833333333333	2,550
2023.3333333333333	2,550
2023.6666666666667	2,550
2023.9166666666667	2,550
2024.1666666666667	2,550
2024.4166666666667	2,550
2024.75	2,550
2025	2,550
2025.25	2,550
2025.5833333333333	2,550
2025.8333333333333	2,550
2026.0833333333333	2,550
2026.4166666666667	2,550
2026.6666666666667	2,550

Rate and persistence

+0.02 Mm³

Mean change per month over 12 months

24 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

Shadow Mountain Lake

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	89.3% 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	89% 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-473.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), Shadow Mountain Lake reservoir records, accessed 2026-10-05, hydrionis.com/reservoirs/reservoir-usbr-473/

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 Shadow Mountain Lake 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

793 monthly observations 1953–2026 Mm³

Spatially aggregatedHigh confidenceSeptember 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 737. 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.