Lk Pillsbury — storage

Storage now, against this reservoir's own record

36.42 Mm³

Stored, September 2025

9th

Percentile among 83 Seps on record

-32.1%

Against the Sep 1991–2020 average

-22.9%

Change over the 12 months to 2025-09

Storage in September 2025 was lower than almost every other Sep on record, ranked against 83 other Seps held for this reservoir.

Storage, 1928–2025

Monthly mean storage

1,100 monthly values, 1928 to 2025

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 1,100 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 1,100 would be longer than this page and unusable with a screen reader.
Period	Lk Pillsbury Nr Potter Valley CA (Mm³)
October 1928	25.0
March 1929	55.3
July 1929	53.2
December 1929	53.1
April 1930	116
September 1930	67.0
February 1931	51.1
June 1931	64.1
November 1931	7.99
March 1932	108
August 1932	99.7
January 1933	46.0
May 1933	116
October 1933	61.6
February 1934	97.2
July 1934	97.4
December 1934	70.0
April 1935	103
September 1935	79.1
January 1936	87.1
June 1936	115
November 1936	56.4
March 1937	96.6
December 1937	93.2
April 1938	102
December 1938	73.2
August 1939	66.1
January 1940	88.3
June 1940	115
December 1940	70.4
September 1941	86.6
March 1942	90.8
July 1942	111
December 1942	89.9
April 1943	114
September 1943	83.7
February 1944	92.3
June 1944	111
December 1944	86.8
April 1945	114
September 1945	72.7
March 1946	98.5
July 1946	98.4
December 1946	70.2
May 1947	115
October 1947	73.4
March 1948	102
July 1948	114
February 1949	75.9
June 1949	115
February 1950	91.1
July 1950	107
March 1951	91.9
December 1951	90.8
April 1952	101
January 1953	94.2
June 1953	115
March 1954	93.4
April 1955	98.1
January 1956	93.7
June 1956	110
May 1957	115
November 1957	85.7
April 1958	93.0
August 1958	92.4
January 1959	70.2
May 1959	115
October 1959	34.0
March 1960	101
July 1960	91.5
December 1960	67.4
April 1961	107
September 1961	70.4
February 1962	73.9
June 1962	104
November 1962	68.6
March 1963	86.4
August 1963	80.3
January 1964	70.2
May 1964	91.4
October 1964	44.6
February 1965	83.1
July 1965	88.6
December 1965	47.7
April 1966	102
September 1966	58.8
January 1967	82.9
June 1967	106
November 1967	17.7
March 1968	89.4
August 1968	76.0
December 1968	48.0
May 1969	107
October 1969	38.2
February 1970	83.6
July 1970	82.3
November 1970	30.1
April 1971	103
September 1971	76.5
January 1972	67.7
June 1972	103
October 1972	38.3
March 1973	83.0
August 1973	75.5
December 1973	84.3
May 1974	106
September 1974	70.5
February 1975	71.2
July 1975	96.1
November 1975	35.6
April 1976	86.8
August 1976	83.6
January 1977	11.8
June 1977	27.4
October 1977	11.8
March 1978	84.7
July 1978	90.8
December 1978	13.1
May 1979	107
September 1979	64.0
February 1980	84.6
June 1980	98.0
November 1980	15.8
April 1981	97.6
August 1981	68.9
January 1982	84.2
May 1982	102
October 1982	53.1
March 1983	86.6
July 1983	77.2
December 1983	85.3
April 1984	86.9
September 1984	67.7
February 1985	75.1
June 1985	98.4
November 1985	11.2
March 1986	76.4
August 1986	67.0
January 1987	22.7
May 1987	75.7
October 1987	34.6
February 1988	72.6
July 1988	52.6
December 1988	38.3
April 1989	97.6
September 1989	56.1
January 1990	42.5
June 1990	97.2
November 1990	28.6
March 1991	75.8
August 1991	74.9
December 1991	27.0
May 1992	95.7
October 1992	45.8
February 1993	76.2
July 1993	90.7
November 1993	27.5
April 1994	67.4
September 1994	42.3
January 1995	73.1
June 1995	96.2
October 1995	71.6
March 1996	81.8
August 1996	79.6
December 1996	66.8
May 1997	85.2
September 1997	49.8
February 1998	80.1
July 1998	94.3
November 1998	37.5
April 1999	89.1
August 1999	74.0
January 2000	48.4
June 2000	93.5
October 2000	49.9
March 2001	81.3
July 2001	75.5
December 2001	75.4
May 2002	77.6
September 2002	47.2
February 2003	74.2
June 2003	96.6
November 2003	36.5
March 2004	78.0
August 2004	67.8
January 2005	72.7
May 2005	97.8
October 2005	59.1
February 2006	69.5
July 2006	77.0
December 2006	37.0
April 2007	81.1
September 2007	36.7
January 2008	62.3
June 2008	69.4
November 2008	24.5
March 2009	75.6
August 2009	59.0
December 2009	33.1
May 2010	86.6
October 2010	56.9
February 2011	67.2
July 2011	87.0
November 2011	36.8
April 2012	83.1
September 2012	38.6
January 2013	67.7
June 2013	56.4
October 2013	24.0
March 2014	63.8
August 2014	57.7
December 2014	61.8
May 2015	46.6
September 2015	21.2
February 2016	68.0
July 2016	47.4
November 2016	38.6
April 2017	86.2
August 2017	56.9
January 2018	30.2
June 2018	78.0
October 2018	48.6
March 2019	72.8
July 2019	87.7
December 2019	53.7
May 2020	65.1
September 2020	42.5
February 2021	39.0
June 2021	42.1
November 2021	65.4
April 2022	67.6
August 2022	51.1
January 2023	73.4
May 2023	70.3
October 2023	42.1
March 2024	72.7
July 2024	58.0
December 2024	72.0
April 2025	71.2
September 2025	36.4

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	56.1	70.7
Feb	62.8	73.7
Mar	72.9	71.6
Apr	83.9	71.2
May	85.8	67.5
Jun	81.1	58.1
Jul	74.0	48.8
Aug	64.2	40.7
Sep	53.7	36.4
Oct	42.8	41.9
Nov	35.7	49.8
Dec	45.6	72.0

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.

Rate and persistence

-0.90 Mm³

Mean drawdown per month over 12 months

11 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

Lk Pillsbury Nr Potter Valley CA

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 Geological Survey — National Water Information System · US Government work — public domain
How the values came to exist	Measured
Period held	1928–2025
Completeness	93.5% 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	94% of the months between 1928 and 2025 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-usgs-11470000.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), Lk Pillsbury Nr Potter Valley CA reservoir records, accessed 2026-10-05, hydrionis.com/reservoirs/reservoir-usgs-11470000/

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 Lk Pillsbury Nr Potter Valley CA 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

1,100 monthly observations 1928–2025 Mm³

Spatially aggregatedHigh confidenceSeptember 2025

Source: USGS — National Water Information System, 11470000. Licence: Open.

Method: Monthly mean of daily reservoir storage published by the USGS in acre-feet and converted to millions of cubic metres. Months with fewer than 20 days of record are not published rather than averaged from a partial month.

Reservoir storage is managed as well as observed: a drawdown may reflect an operating rule, flood-control rule curve or scheduled release rather than a shortage. Compare a month against the same month in other years, and do not read a fall as a supply signal without knowing the operating regime.

Retrieved 1 October 2026.

Monthly mean of daily reservoir storage published by the USGS in acre-feet and converted to millions of cubic metres. Months with fewer than 20 days of record are not published rather than averaged from a partial month.