Howard Prairie Lake — storage

Storage now, against this reservoir's own record

41.84 Mm³

Stored, August 2026

32nd

Percentile among 61 Augs on record

-11.6%

Against the Aug 1991–2020 average

-33.2%

Change over the 12 months to 2026-08

Storage in August 2026 was around the middle of the Aug record, ranked against 61 other Augs held for this reservoir.

Storage, 1966–2026

Monthly mean storage

724 monthly values, 1966 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 724 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 724 would be longer than this page and unusable with a screen reader.
Period	Howard Prairie Lake (Mm³)
May 1966	63.6
August 1966	51.8
November 1966	43.2
February 1967	42.3
May 1967	64.2
August 1967	66.2
November 1967	57.0
February 1968	47.6
May 1968	49.0
August 1968	34.9
November 1968	23.6
February 1969	24.3
May 1969	60.7
August 1969	63.6
November 1969	52.0
February 1970	67.3
May 1970	74.8
August 1970	64.9
November 1970	54.7
February 1971	65.9
June 1971	77.3
September 1971	64.2
December 1971	59.4
March 1972	77.9
June 1972	74.3
September 1972	62.3
December 1972	55.5
March 1973	56.7
June 1973	60.6
September 1973	46.4
December 1973	48.6
March 1974	74.8
June 1974	74.5
September 1974	61.6
December 1974	51.2
March 1975	52.1
June 1975	76.2
September 1975	63.7
December 1975	60.3
March 1976	64.9
June 1976	73.7
September 1976	61.2
December 1976	51.3
March 1977	43.0
June 1977	40.7
September 1977	28.4
December 1977	28.1
March 1978	49.8
June 1978	59.9
September 1978	49.2
December 1978	41.7
March 1979	47.2
June 1979	72.7
September 1979	60.2
December 1979	59.8
March 1980	74.4
June 1980	74.4
September 1980	63.0
December 1980	54.6
March 1981	54.0
July 1981	48.1
October 1981	35.7
January 1982	53.6
April 1982	76.5
July 1982	70.3
October 1982	57.3
January 1983	55.1
April 1983	75.9
July 1983	72.2
October 1983	61.9
January 1984	70.1
April 1984	77.9
July 1984	72.4
October 1984	61.9
January 1985	64.3
April 1985	73.2
July 1985	69.6
October 1985	57.9
January 1986	52.0
April 1986	74.8
July 1986	69.3
October 1986	57.1
January 1987	50.2
April 1987	55.5
July 1987	47.6
October 1987	39.1
January 1988	32.4
April 1988	33.9
July 1988	29.1
October 1988	17.8
January 1989	13.2
April 1989	35.0
July 1989	47.1
October 1989	39.4
January 1990	33.8
April 1990	40.0
July 1990	39.0
October 1990	30.3
January 1991	26.1
April 1991	29.2
August 1991	36.4
November 1991	27.6
February 1992	23.9
May 1992	20.5
August 1992	9.17
November 1992	8.21
February 1993	3.34
May 1993	38.9
August 1993	44.0
November 1993	41.0
February 1994	36.1
May 1994	32.9
August 1994	20.2
November 1994	14.6
February 1995	19.8
May 1995	58.7
August 1995	62.1
November 1995	52.0
February 1996	73.5
May 1996	76.2
August 1996	67.5
November 1996	61.0
February 1997	76.7
May 1997	75.9
August 1997	66.5
November 1997	57.3
February 1998	60.1
May 1998	77.0
August 1998	68.0
November 1998	58.8
February 1999	60.4
May 1999	74.0
August 1999	67.1
November 1999	56.1
February 2000	52.7
May 2000	72.9
August 2000	62.5
November 2000	50.9
February 2001	41.9
May 2001	45.0
September 2001	28.2
December 2001	21.4
March 2002	26.4
June 2002	43.3
September 2002	30.0
December 2002	22.2
March 2003	30.6
June 2003	51.3
September 2003	38.7
December 2003	31.1
March 2004	39.5
June 2004	63.3
September 2004	49.5
December 2004	43.7
March 2005	40.5
June 2005	52.9
September 2005	40.7
December 2005	43.3
March 2006	72.9
June 2006	74.4
September 2006	60.5
December 2006	58.5
March 2007	70.3
June 2007	72.1
September 2007	58.4
December 2007	55.0
March 2008	54.6
June 2008	74.9
September 2008	62.3
December 2008	55.4
March 2009	55.6
June 2009	73.7
September 2009	60.0
December 2009	52.6
March 2010	47.7
June 2010	59.4
September 2010	48.1
December 2010	45.1
March 2011	54.2
June 2011	74.9
October 2011	60.6
January 2012	55.3
April 2012	60.2
July 2012	64.4
October 2012	50.9
January 2013	47.6
April 2013	59.4
July 2013	54.7
October 2013	42.7
January 2014	42.1
April 2014	43.4
July 2014	31.7
October 2014	20.5
January 2015	23.1
April 2015	31.9
July 2015	20.3
October 2015	10.2
January 2016	14.1
April 2016	49.5
July 2016	45.2
October 2016	35.0
January 2017	38.1
April 2017	72.8
July 2017	69.1
October 2017	56.6
January 2018	50.7
April 2018	47.3
July 2018	38.0
October 2018	25.5
January 2019	22.2
April 2019	32.6
July 2019	34.1
October 2019	24.9
January 2020	21.7
April 2020	20.6
July 2020	13.8
October 2020	4.93
January 2021	6.18
April 2021	7.07
July 2021	3.59
November 2021	3.09
February 2022	4.80
May 2022	11.8
August 2022	5.03
November 2022	5.19
February 2023	13.0
May 2023	35.0
August 2023	29.3
November 2023	25.4
February 2024	28.8
May 2024	41.1
August 2024	33.6
November 2024	30.4
February 2025	39.1
May 2025	70.5
August 2025	62.7
November 2025	58.4
February 2026	57.7
May 2026	55.6
August 2026	41.8

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	40.6	59.4
Feb	42.0	57.7
Mar	45.1	59.4
Apr	51.6	58.5
May	56.2	55.6
Jun	55.4	51.3
Jul	51.8	46.8
Aug	47.3	41.8
Sep	43.2	59.6
Oct	40.6	58.2
Nov	39.7	58.4
Dec	39.3	58.5

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

705 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 705 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 705 would be longer than this page and unusable with a screen reader.
Period	Howard Prairie Lake (m)
1967.9166666666667	1,377
1968.1666666666667	1,376
1968.4166666666667	1,375
1968.6666666666667	1,373
1968.9166666666667	1,371
1969.1666666666667	1,372
1969.4166666666667	1,379
1969.6666666666667	1,378
1969.9166666666667	1,376
1970.1666666666667	1,379
1970.3333333333333	1,380
1970.5833333333333	1,378
1970.8333333333333	1,377
1971.0833333333333	1,379
1971.3333333333333	1,380
1971.5833333333333	1,379
1971.8333333333333	1,377
1972.0833333333333	1,379
1972.3333333333333	1,380
1972.5833333333333	1,379
1972.8333333333333	1,377
1973.0833333333333	1,377
1973.3333333333333	1,378
1973.5833333333333	1,376
1973.8333333333333	1,375
1974.0833333333333	1,380
1974.3333333333333	1,380
1974.5833333333333	1,379
1974.75	1,377
1975	1,376
1975.25	1,377
1975.5	1,380
1975.75	1,378
1976	1,378
1976.25	1,379
1976.5	1,379
1976.75	1,377
1977	1,376
1977.25	1,375
1977.5	1,374
1977.75	1,372
1978	1,374
1978.25	1,377
1978.5	1,377
1978.75	1,376
1979	1,375
1979.1666666666667	1,376
1979.4166666666667	1,379
1979.6666666666667	1,378
1979.9166666666667	1,378
1980.1666666666667	1,380
1980.4166666666667	1,380
1980.6666666666667	1,378
1980.9166666666667	1,377
1981.1666666666667	1,377
1981.4166666666667	1,377
1981.6666666666667	1,374
1981.9166666666667	1,375
1982.1666666666667	1,380
1982.4166666666667	1,380
1982.6666666666667	1,378
1982.9166666666667	1,377
1983.1666666666667	1,379
1983.4166666666667	1,380
1983.6666666666667	1,378
1983.8333333333333	1,378
1984.0833333333333	1,379
1984.3333333333333	1,380
1984.5833333333333	1,379
1984.8333333333333	1,378
1985.0833333333333	1,378
1985.3333333333333	1,380
1985.5833333333333	1,378
1985.8333333333333	1,377
1986.0833333333333	1,377
1986.3333333333333	1,380
1986.5833333333333	1,378
1986.8333333333333	1,377
1987.0833333333333	1,376
1987.3333333333333	1,377
1987.5833333333333	1,375
1987.8333333333333	1,374
1988.0833333333333	1,373
1988.25	1,373
1988.5	1,373
1988.75	1,370
1989	1,369
1989.25	1,374
1989.5	1,376
1989.75	1,374
1990	1,373
1990.25	1,375
1990.5	1,374
1990.75	1,373
1991	1,372
1991.25	1,373
1991.5	1,375
1991.75	1,373
1992	1,372
1992.25	1,371
1992.5	1,368
1992.75	1,367
1992.9166666666667	1,367
1993.1666666666667	1,367
1993.4166666666667	1,376
1993.6666666666667	1,375
1993.9166666666667	1,375
1994.1666666666667	1,374
1994.4166666666667	1,373
1994.6666666666667	1,369
1994.9166666666667	1,368
1995.1666666666667	1,373
1995.4166666666667	1,378
1995.6666666666667	1,377
1995.9166666666667	1,377
1996.1666666666667	1,380
1996.4166666666667	1,380
1996.6666666666667	1,378
1996.9166666666667	1,379
1997.1666666666667	1,380
1997.3333333333333	1,380
1997.5833333333333	1,379
1997.8333333333333	1,377
1998.0833333333333	1,378
1998.3333333333333	1,380
1998.5833333333333	1,379
1998.8333333333333	1,378
1999.0833333333333	1,378
1999.3333333333333	1,380
1999.5833333333333	1,379
1999.8333333333333	1,377
2000.0833333333333	1,377
2000.3333333333333	1,379
2000.5833333333333	1,378
2000.8333333333333	1,376
2001.0833333333333	1,375
2001.3333333333333	1,375
2001.5833333333333	1,373
2001.75	1,372
2002	1,371
2002.25	1,374
2002.5	1,374
2002.75	1,372
2003	1,371
2003.25	1,375
2003.5	1,376
2003.75	1,374
2004	1,373
2004.25	1,377
2004.5	1,378
2004.75	1,376
2005	1,375
2005.25	1,375
2005.5	1,376
2005.75	1,374
2006	1,377
2006.25	1,380
2006.4166666666667	1,380
2006.6666666666667	1,378
2006.9166666666667	1,378
2007.1666666666667	1,379
2007.4166666666667	1,379
2007.6666666666667	1,378
2007.9166666666667	1,377
2008.1666666666667	1,377
2008.4166666666667	1,380
2008.6666666666667	1,378
2008.9166666666667	1,377
2009.1666666666667	1,377
2009.4166666666667	1,380
2009.6666666666667	1,378
2009.9166666666667	1,377
2010.1666666666667	1,376
2010.4166666666667	1,378
2010.6666666666667	1,376
2010.8333333333333	1,376
2011.0833333333333	1,376
2011.3333333333333	1,380
2011.5833333333333	1,379
2011.8333333333333	1,378
2012.0833333333333	1,377
2012.3333333333333	1,379
2012.5833333333333	1,378
2012.8333333333333	1,376
2013.0833333333333	1,376
2013.3333333333333	1,378
2013.5833333333333	1,376
2013.8333333333333	1,375
2014.0833333333333	1,375
2014.3333333333333	1,375
2014.5833333333333	1,372
2014.8333333333333	1,371
2015.0833333333333	1,373
2015.3333333333333	1,373
2015.5	1,371
2015.75	1,368
2016	1,369
2016.25	1,376
2016.5	1,375
2016.75	1,374
2017	1,374
2017.25	1,379
2017.5	1,379
2017.75	1,377
2018	1,376
2018.25	1,376
2018.5	1,374
2018.75	1,372
2019	1,371
2019.25	1,373
2019.5	1,374
2019.75	1,372
2019.9166666666667	1,371
2020.1666666666667	1,371
2020.4166666666667	1,370
2020.6666666666667	1,366
2020.9166666666667	1,366
2021.1666666666667	1,366
2021.4166666666667	1,366
2021.6666666666667	1,365
2021.9166666666667	1,365
2022.1666666666667	1,366
2022.4166666666667	1,368
2022.6666666666667	1,366
2022.9166666666667	1,366
2023.1666666666667	1,369
2023.4166666666667	1,374
2023.6666666666667	1,372
2023.9166666666667	1,372
2024.1666666666667	1,373
2024.3333333333333	1,375
2024.5833333333333	1,373
2024.8333333333333	1,373
2025.0833333333333	1,374
2025.3333333333333	1,379
2025.5833333333333	1,378
2025.8333333333333	1,378
2026.0833333333333	1,377
2026.3333333333333	1,377
2026.5833333333333	1,375

Rate and persistence

-1.74 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

Howard Prairie 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	1966–2026
Completeness	98.9% 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 1966 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-7182.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), Howard Prairie Lake reservoir records, accessed 2026-09-02, hydrionis.com/reservoirs/reservoir-usbr-7182/

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 Howard Prairie 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

724 monthly observations 1966–2026 Mm³

Spatially aggregatedHigh confidenceAugust 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 130954. 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.