Storm overflow register · United Utilities

Prospect And Oughterside Prspo sewage works: storm overflow spills 2025

Prospect And Oughterside Prspo sewage treatment works, run by United Utilities, has 1 monitored storm overflow discharging to Salterwath Beck. In 2025 it recorded 114 spills totalling 643 hours, against 145 spills and 662 hours in 2024. By hours spilling, it ranks 79 of 289 United Utilities works, where 1 spilled longest.

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.

JanFebMarAprMayJunJulAugSepOctNovDecProspect and…18 spills, 8.7 h, 1 Jan to 1 Jan22 spills, 11 h, 5 Jan to 6 Jan6 spills, 1.4 h, 13 Jan to 13 Jan6 spills, 1.1 h, 23 Jan to 24 Jan4 spills, 1.4 h, 25 Jan to 26 Jan2 spills, 0.9 h, 27 Jan to 27 Jan8 spills, 5.9 h, 4 Feb to 4 Feb3 spills, 3.4 h, 21 Feb to 21 Feb7 spills, 3.4 h, 23 Feb to 23 Feb3 spills, 1.7 h, 24 Feb to 24 Feb3 spills, 2.1 h, 27 Mar to 28 Mar4 spills, 1.2 h, 29 Mar to 29 Mar2 spills, 0.8 h, 16 Apr to 16 Apr2 spills, 1.1 h, 18 Apr to 18 Apr6 spills, 1.9 h, 24 May to 24 May2 spills, 0.1 h, 26 May to 26 May5 spills, 8.2 h, 29 May to 29 May4 spills, 5.5 h, 3 Jun to 3 Jun7 spills, 4 h, 4 Jun to 5 Jun6 Jun 2025 05:41 GMT, 40 min2 spills, 1.8 h, 7 Jun to 7 Jun8 Jun 2025 19:59 GMT, 64 min2 spills, 6.4 h, 9 Jun to 10 Jun12 Jun 2025 19:17 GMT, 28 min18 spills, 13.1 h, 14 Jun to 14 Jun5 spills, 3.1 h, 21 Jun to 22 Jun5 spills, 3.5 h, 24 Jun to 24 Jun3 spills, 3.5 h, 26 Jun to 26 Jun6 spills, 1.5 h, 27 Jun to 27 Jun4 spills, 0.1 h, 28 Jun to 28 Jun2 spills, 1.1 h, 1 Jul to 1 Jul2 Jul 2025 12:25 GMT, 44 min4 spills, 9.4 h, 4 Jul to 4 Jul2 spills, 1.9 h, 6 Jul to 6 Jul2 spills, 0.5 h, 8 Jul to 9 Jul14 Jul 2025 01:26 GMT, 3.1 h7 spills, 8.2 h, 15 Jul to 15 Jul5 spills, 7 h, 20 Jul to 21 Jul3 spills, 2.1 h, 3 Aug to 3 Aug4 spills, 3.6 h, 4 Aug to 4 Aug2 spills, 0.2 h, 26 Aug to 26 Aug6 spills, 1.5 h, 28 Aug to 29 Aug1 Sep 2025 08:35 GMT, 42 min9 spills, 3.8 h, 3 Sep to 3 Sep5 Sep 2025 05:36 GMT, 33 min7 spills, 1.7 h, 8 Sep to 8 Sep8 spills, 3.7 h, 10 Sep to 11 Sep29 spills, 16.1 h, 12 Sep to 13 Sep10 spills, 24.9 h, 14 Sep to 16 Sep3 spills, 2.7 h, 17 Sep to 17 Sep26 spills, 52.5 h, 19 Sep to 21 Sep27 Sep 2025 18:04 GMT, 42 min3 spills, 0.1 h, 1 Oct to 1 Oct29 spills, 16.7 h, 2 Oct to 4 Oct9 spills, 3.1 h, 7 Oct to 7 Oct7 spills, 1 h, 21 Oct to 21 Oct26 Oct 2025 14:29 GMT, 37 min3 spills, 1.9 h, 27 Oct to 28 Oct2 spills, 0.1 h, 29 Oct to 29 Oct31 Oct 2025 01:01 GMT, 56 min12 spills, 7.3 h, 1 Nov to 2 Nov56 spills, 64.9 h, 3 Nov to 5 Nov10 spills, 3.8 h, 9 Nov to 10 Nov2 spills, 1.5 h, 11 Nov to 11 Nov23 spills, 39 h, 12 Nov to 14 Nov21 spills, 35.7 h, 22 Nov to 24 Nov16 spills, 15.2 h, 27 Nov to 28 Nov12 spills, 8.2 h, 29 Nov to 29 Nov33 spills, 42.3 h, 1 Dec to 3 Dec46 spills, 57.5 h, 5 Dec to 10 Dec12 spills, 54.8 h, 13 Dec to 16 Dec120 spills, 41.9 h, 17 Dec to 20 Dec12 spills, 1.3 h, 22 Dec to 22 Dec

Hours spilling by month, 2025

050100150200Jan 2025: 25 hours spillingJanFeb 2025: 14 hours spillingFebMar 2025: 3.2 hours spillingMarApr 2025: 1.9 hours spillingAprMay 2025: 10 hours spillingMayJun 2025: 45 hours spillingJunJul 2025: 32 hours spillingJulAug 2025: 7.4 hours spillingAugSep 2025: 107 hours spillingSepOct 2025: 25 hours spillingOctNov 2025: 176 hours spillingNovDec 2025: 198 hours spillingDec
Hours, measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDuration
13 Dec 2025, 22:40Prospect and Oughterside WwTW Prspo2.1 days
4 Nov 2025, 02:01Prospect and Oughterside WwTW Prspo21.9 h
1 Dec 2025, 15:42Prospect and Oughterside WwTW Prspo21.1 h
17 Dec 2025, 15:15Prospect and Oughterside WwTW Prspo20.3 h
7 Dec 2025, 17:07Prospect and Oughterside WwTW Prspo16.9 h

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.

This works serves fewer than 2,000 people, or was not matched to a UWWTD report, so its size is not published. The population equivalent above is a placeholder of 1,000. Enter the population served if you know it.

Volume, central estimate11,012 m³range 4,386 - 27,647 m³
In litres11.0 millionrange 4.4 million - 27.6 million L
Olympic swimming pools4.4at 2,500 m³ each
Organic load, as people's raw sewage16,518person-days of untreated BOD

Assumed spill rate while spilling: 1.9 - 11.9 L/s (central 4.8 L/s), from a dry-weather flow of 1.9 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 175 kg991 kg5,529 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 461 kg4,680 kg19,933 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 8.3 kg69 kg257 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 5.3 kg29 kg149 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 438.6 billion organisms11.0 trillion organisms276.5 trillion 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.

Prospect and Oughterside WwTW Prspo

Inlet overflow at sewage works · discharges to Salterwath Beck

Spills 2025
114 (643 hours) · down 21% on 2024
Spills 2024
145 (662 hours)
Long-term average
127.9 spills a year (monitored since 2017)
Monitor uptime
100% of the year
High-spill reason (company)
Performance - SW Infiltration
Investigation
No investigation activity in reporting period
Improvement
Env Act (SODRP) improvement ongoing
Bathing water
Allonby
WFD catchment
Ellen (lower) (GB112075073640)
Outlet location
NY1170040020 (OS grid reference) · View on Apple Maps
EA ID / permit
UUP01588 · 017570073 · company name: PROSPECT & OUGHTERSIDE WwTW

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 United Utilities 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.