Storm overflow register · Yorkshire Water

Skipton sewage works: storm overflow spills 2025

Skipton sewage treatment works, run by Yorkshire Water, has 2 monitored storm overflows discharging to River Aire. In 2025 they recorded 173 spills totalling 1,334 hours, against 201 spills and 1,417 hours in 2024. By hours spilling, it ranks 22 of 283 Yorkshire Water works, where 1 spilled longest.

Works size: 19,421 population equivalent (SKIPTON STW, UWWTD 2018). Used for the spill volume estimate.

Every spill in 2025

Each blue mark is one spill, placed by when it started and sized by how long it lasted. Hover over a mark for the date and duration.

JanFebMarAprMayJunJulAugSepOctNovDecSkipton Sewage…1 Jan 2025 00:00 GMT, 21.8 h9 spills, 53.8 h, 5 Jan to 8 Jan21 spills, 18.3 h, 13 Jan to 14 Jan21 Jan 2025 07:45 GMT, 45 min6 spills, 9.3 h, 23 Jan to 24 Jan3 spills, 15.5 h, 26 Jan to 28 Jan3 spills, 4.8 h, 19 Feb to 20 Feb21 Feb 2025 20:15 GMT, 30 min3 spills, 5.8 h, 23 Feb to 23 Feb26 Feb 2025 07:15 GMT, 75 min7 Mar 2025 01:00 GMT, 15 min2 spills, 4.3 h, 22 Mar to 23 Mar24 May 2025 00:15 GMT, 75 min3 spills, 1.5 h, 25 May to 25 May26 May 2025 17:00 GMT, 6.3 h4 spills, 3 h, 29 May to 29 May30 May 2025 06:00 GMT, 75 min31 May 2025 14:00 GMT, 60 min2 spills, 5 h, 3 Jun to 3 Jun3 spills, 3.5 h, 6 Jun to 6 Jun7 Jun 2025 08:00 GMT, 90 min8 Jun 2025 12:45 GMT, 15 min2 spills, 5.5 h, 9 Jun to 10 Jun3 spills, 4 h, 22 Jun to 22 Jun2 Jul 2025 07:45 GMT, 30 min2 spills, 3.3 h, 6 Jul to 6 Jul3 spills, 6.8 h, 15 Jul to 15 Jul19 Jul 2025 16:15 GMT, 2 h20 Jul 2025 14:15 GMT, 9.5 h23 Jul 2025 18:00 GMT, 2.5 h2 spills, 1.8 h, 4 Aug to 4 Aug2 spills, 2.3 h, 30 Aug to 30 Aug4 spills, 4.3 h, 3 Sep to 4 Sep7 Sep 2025 13:45 GMT, 60 min8 Sep 2025 15:00 GMT, 30 min8 spills, 11.8 h, 11 Sep to 13 Sep11 spills, 41.8 h, 14 Sep to 17 Sep10 spills, 36.5 h, 20 Sep to 22 Sep2 spills, 5.3 h, 27 Sep to 28 Sep2 spills, 2.5 h, 1 Oct to 1 Oct10 spills, 44.5 h, 2 Oct to 5 Oct5 spills, 15.5 h, 19 Oct to 20 Oct2 spills, 1 h, 21 Oct to 21 Oct3 spills, 1.5 h, 23 Oct to 23 Oct24 Oct 2025 20:45 GMT, 60 min7 spills, 5.3 h, 26 Oct to 27 Oct15 spills, 13.3 h, 28 Oct to 29 Oct6 spills, 4.5 h, 30 Oct to 1 Nov15 spills, 16.8 h, 3 Nov to 5 Nov3 spills, 3.3 h, 9 Nov to 10 Nov37 spills, 69 h, 11 Nov to 16 Nov10 spills, 18.3 h, 18 Nov to 19 Nov22 Nov 2025 04:00 GMT, 75 min8 spills, 15.3 h, 23 Nov to 24 Nov10 spills, 11 h, 27 Nov to 29 Nov21 spills, 21.3 h, 1 Dec to 2 Dec3 spills, 4.5 h, 4 Dec to 4 Dec38 spills, 96 h, 5 Dec to 11 Dec12 Dec 2025 10:45 GMT, 75 min11 spills, 21.5 h, 14 Dec to 16 Dec18 spills, 24.3 h, 17 Dec to 19 Dec3 spills, 4.3 h, 21 Dec to 22 DecSkipton Sewage…76 spills, 42.6 h, 1 Jan to 3 Jan120 spills, 57.7 h, 5 Jan to 8 Jan33 spills, 10.6 h, 14 Jan to 15 Jan17 spills, 2.9 h, 24 Jan to 24 Jan124 spills, 37.2 h, 27 Jan to 28 Jan14 spills, 0.6 h, 26 May to 27 May10 spills, 2.3 h, 29 May to 29 May15 spills, 1.5 h, 3 Jun to 3 Jun37 spills, 4.2 h, 10 Jun to 10 Jun8 spills, 4.7 h, 15 Jul to 15 Jul5 spills, 8 h, 20 Jul to 21 Jul2 spills, 5 h, 12 Sep to 12 Sep59 spills, 39.6 h, 15 Sep to 17 Sep19 spills, 36.5 h, 20 Sep to 21 Sep5 spills, 2.8 h, 27 Sep to 28 Sep50 spills, 42.2 h, 3 Oct to 5 Oct37 spills, 15.9 h, 19 Oct to 20 Oct93 spills, 17.4 h, 28 Oct to 29 Oct82 spills, 14 h, 4 Nov to 5 Nov158 spills, 72.8 h, 11 Nov to 16 Nov83 spills, 23.2 h, 18 Nov to 19 Nov62 spills, 15.5 h, 23 Nov to 24 Nov28 Nov 2025 14:02 GMT, 18 min13 spills, 2.4 h, 29 Nov to 29 Nov46 spills, 23.9 h, 1 Dec to 2 Dec140 spills, 106.5 h, 5 Dec to 11 Dec52 spills, 19.3 h, 15 Dec to 16 Dec155 spills, 28.5 h, 17 Dec to 19 Dec

Estimated spill volume by month, 2025

Hours spilling each month × the estimated spill rate for a works of this size. The bars are central estimates and the whiskers show the low-high range. Method.

0100k200k300kJan 2025: 270 h spilling ≈ 89,947 m³ (range 35,828-225,816 m³)JanFeb 2025: 12 h spilling ≈ 4,060 m³ (range 1,617-10,192 m³)FebMar 2025: 4.5 h spilling ≈ 1,497 m³ (range 596-3,759 m³)MarApr 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AprMay 2025: 17 h spilling ≈ 5,690 m³ (range 2,267-14,286 m³)MayJun 2025: 26 h spilling ≈ 8,486 m³ (range 3,380-21,303 m³)JunJul 2025: 37 h spilling ≈ 12,379 m³ (range 4,931-31,078 m³)JulAug 2025: 4.0 h spilling ≈ 1,331 m³ (range 530-3,342 m³)AugSep 2025: 185 h spilling ≈ 61,495 m³ (range 24,495-154,387 m³)SepOct 2025: 161 h spilling ≈ 53,576 m³ (range 21,340-134,504 m³)OctNov 2025: 267 h spilling ≈ 88,683 m³ (range 35,324-222,641 m³)NovDec 2025: 351 h spilling ≈ 116,835 m³ (range 46,538-293,318 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
5 Jan 2025, 17:50Skipton Sewage Treatment Works2.2 days6,906 - 43,526 m³
6 Dec 2025, 18:58Skipton Sewage Treatment Works1.8 days5,594 - 35,255 m³
3 Oct 2025, 12:26Skipton Sewage Treatment Works1.5 days4,838 - 30,493 m³
3 Oct 2025, 12:15Skipton Sewage Treatment Works1.5 days4,672 - 29,449 m³
6 Dec 2025, 12:45Skipton Sewage Treatment Works1.4 days4,407 - 27,778 m³

Estimated 2025 spill volume and pollution

Estimate, not a measurement. Monitors record how long an overflow spills, not how much. This calculator back-calculates a spill rate from the size of the works, using the Environment Agency's permit formulae, and multiplies it by published storm-sewage concentrations. How it works.

Volume, central estimate444,012 m³range 176,859 - 1.1 million m³
In litres444.0 millionrange 176.9 million - 1.1 billion L
Olympic swimming pools178at 2,500 m³ each
Organic load, as people's raw sewage666,018person-days of untreated BOD

Assumed spill rate while spilling: 36.8 - 232.1 L/s (central 92.4 L/s), from a dry-weather flow of 36.8 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 7,074 kg39,961 kg222,942 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 18,570 kg188,705 kg803,706 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 336 kg2,797 kg10,367 kg 1.9 / 6.3 / 9.3 mg/L
Low: Germany, Brombach 2005; typical/high: Paris range 3.3-9.3 midpoint and top, Gasperi 2012 (via botturi); no UK value found
Total phosphorus 212 kg1,154 kg6,019 kg 1.2 / 2.6 / 5.4 mg/L
Low/high: Paris, Gasperi 2012; typical: Slovakia (via botturi). UK figure of 10 mg/L treated as an outlier
E. coli 17.7 trillion organisms444.0 trillion organisms1.1 × 10¹⁶ organisms 10,000 / 100,000 / 1.0 million per 100 mL
Median range at CSO and retention-tank outlets, Stott et al. 2018 (via botturi); typical = log midpoint

Low combines the low spill rate with low concentrations, and high combines high with high, so the true figure is very likely inside the range. Long spills become more diluted as they go on, so the central figure tends to overstate the load of long events. The calculator does not estimate the effect on the receiving water, which depends on river flow or tide at the time of the spill.

Skipton Sewage Treatment Works

Inlet overflow at sewage works · discharges to River Aire

Spills 2025
111 (696 hours) · down 3% on 2024
Spills 2024
115 (526 hours)
Long-term average
99.2 spills a year (monitored since 2020)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - hydraulic capacity
Investigation
UWWTR investigation ongoing, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Aire (Eshton Beck to R Worth) (GB104027063033)
Outlet location
SD9859049710 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS00637 · 2838 · company name: SKIPTON/STW/6XDWF OVERFLOW

Skipton Sewage Treatment Works

Storm tank at sewage works · discharges to River Aire

Spills 2025
62 (638 hours) · down 28% on 2024
Spills 2024
86 (892 hours)
Long-term average
73.0 spills a year (monitored since 2020)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - hydraulic capacity
Investigation
UWWTR investigation ongoing, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Aire (Eshton Beck to R Worth) (GB104027063033)
Outlet location
SD9859049710 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS00636 · 2838 · company name: SKIPTON/STW/3XDWF OVERFLOW

How the estimate works

  1. Dry-weather flow (DWF) = population × water use per person × (1 + infiltration). Water use is 136.5 L per person per day, England's per-capita consumption for 2024-25 [EA]. Infiltration of groundwater into sewers is taken as 0-40% of that flow [Escritt, via HBF]. The Environment Agency defines DWF as PG + I + E [EA].
  2. Population. The size of each works comes from the load entering it as reported under the Urban Waste Water Treatment Directive, in population equivalents (1 p.e. = 60 g of BOD a day) [UWWTD]. We treat population equivalent as population. That overstates flow where trade effluent adds load, and no official source links the two. Works serving fewer than 2,000 p.e. are not reported, so their size has to be entered by hand.
  3. Low spill rate = DWF. This is the method used by Giakoumis & Voulvoulis (2026), which they note likely underestimates storm loads [G&V].
  4. High spill rate = Formula A − flow to full treatment = (DWF + 1360P) − 3DWF. This is the largest flow the permit expects the storm tanks to handle before it passes on to treatment or overflows [EA]. The central rate is the geometric mean of the low and high rates.
  5. Volume = spill rate × hours spilling, with hours taken from the event duration monitor.
  6. Pollution = volume × published storm-sewage concentrations [Botturi et al.] [US EPA]. Organic load is also shown as person-days of untreated sewage at 60 g of BOD per person per day [UWWTD].

What this cannot tell you. It gives no real flow for any single spill, and no effect on the river or sea, which depends on the flow, tide and the other pressures on the water at the time. It gives no figure for spills from overflows on the sewer network, which serve catchments of unknown size. It is a way to put hours into rough physical terms, not a substitute for flow monitoring.

Sources

  1. EA: Water companies - environmental permits for storm overflows and emergency overflows
  2. EA: Water resources 2024 to 2025 - per capita consumption
  3. HBF: Foul sewer design - historic conventions (citing Escritt 1984 on infiltration)
  4. Giakoumis & Voulvoulis (2026), Environ. Sci.: Water Res. Technol., doi:10.1039/D5EW00860C
  5. Botturi et al. (2021), Crit. Rev. Environ. Sci. Technol. 51:1585 - CSO quality review, Table 2
  6. US EPA (2004) Report to Congress on CSOs and SSOs, chapter 4
  7. Urban Waste Water Treatment Directive, Article 2(6): 1 p.e. = 60 g BOD5/day
  8. Olympic-size swimming pool: 2,500 m³ at the nominal 2 m depth

← All Yorkshire Water works · Contains Environment Agency data licensed under the Open Government Licence v3.0. Spill start and stop times: © Environment Agency copyright and/or database right 2026. All rights reserved. They are water-company data and have not been verified by the Environment Agency. Works size: EEA Waterbase UWWTD. How to read the data.