Dwr Cymru Welsh Water · overflow Hermon Street Treorchy Storm Overflow
No active event
Recorded by the operator as Rhondda Fawr River. The outfall is 10 m from the Afon Rhondda on the Ordnance Survey river network, which is the river this page groups it under.
The monitor for overflow Hermon Street Treorchy Storm Overflow (operator listed as Dwr Cymru Welsh Water) reports no current spill. The data records 38 spill events totalling 3 days in the last 30 days.
📍 51.65715°, -3.50007°
189
spill events
240h
cumulative discharge
28.8 h
longest single event
2026-05-14
first event on record
In the last 30 days this overflow recorded 63h of discharge. Across Dwr Cymru Welsh Water's 2,359 monitored overflows the median was 0h. This site is in the top 2% by 30-day spill duration.
12 other overflows discharge into the Rhondda Fawr River. Combined recorded discharge in the last 30 days: 35h.
What the water company itself reported in its annual returns for this overflow, year by year, as republished by The Rivers Trust. Hours are the total reported discharge duration; monitor working is the share of the year the event monitor was operating (a figure of 0% may mean no usable monitoring data rather than no spills). These figures are the operator's own reporting, not our measurement, and our live record above begins on 6 May 2026.
| Year | Spills counted | Hours | Monitor working | Matched by |
|---|---|---|---|---|
| 2021 | 154 | 1,803h | 100% | location, 69 m (medium confidence) |
| 2022 | 146 | 1,687h | 100% | location, 1 m (high confidence) |
| 2023 | 177 | 2,276h | 100% | location, 1 m (high confidence) |
| 2024 | 184 | 2,217h | 100% | location, 1 m (high confidence) |
| 2025 | 154 | 2,156h | 100% | location, 1 m (high confidence) |
Source: the operator's annual returns, as republished by The Rivers Trust (Event Duration Monitoring, storm overflows, 2021 to 2025, England and Wales). Contains public sector information licensed under the Open Government Licence v3.0. Produced by The Rivers Trust. © Environment Agency copyright and/or database right 2025. All rights reserved. © Dwr Cymru/Welsh Water. © Hafren Dyfrdwy. The rows carry no identifier shared with our overflow list, so each is matched by location: the nearest row within 150 m, or by permit reference where a year could not be placed. The distance is shown per row, nothing is forced, and where several rows sit at one location their figures are added together. Years where the match is uncertain, or close to another overflow's row, are left out here rather than risk showing another overflow's figures.
No surface-water sampling points within 5 km.
The record above is verifiable from public Environment Agency and water-company data. Three official accountability channels — pre-filled with the evidence on this page.
If you can see foam, sewage debris, dead fish, or smell something wrong — submit a citizen report. Confirmed reports are added to the Truth Engine and strengthen the public record on this overflow.
📷 Report what you saw →The official complaints route. Most companies require submission through their web form rather than email — open the form, then paste the pre-filled letter.
Subject: Storm overflow Hermon Street Treorchy Storm Overflow on the Rhondda Fawr River: request for information Dear Dwr Cymru Welsh Water, I am writing about storm overflow Hermon Street Treorchy Storm Overflow on the Rhondda Fawr River. Environment Agency storm overflow monitoring data for overflow Hermon Street Treorchy Storm Overflow on the Rhondda Fawr River (operator listed as Dwr Cymru Welsh Water) records 38 spill events starting between 17 September 2026 and 17 October 2026; the 32 with a published end time total 3 days. The most recent recorded event started on 16 October 2026 at 03:45 UTC. As of 17 October 2026 at 20:39 UTC, the monitor does not report the overflow as spilling. Further details from the public record: - On the Afon Rhondda, per the OS Open Rivers network (Ordnance Survey, Open Government Licence) - Location: 51.65715, -3.50007 - Sources: Environment Agency National Storm Overflow Hub and Water Quality Archive (Open Government Licence v3.0), cross-referenced via River Truth (https://rivertruth.co.uk/overflow/13652) These figures are taken from public monitoring data as published and may be revised by the publisher. They are not a finding that any permit condition has been breached. [Add your personal context here, for example how you use this stretch of water.] Please could you tell me: 1. Whether the monitoring record summarised above is accurate and complete 2. What caused the recorded spill events 3. What work, if any, is planned at this overflow, and on what timeline 4. What measures are in place to reduce spills from this overflow in future [Delete if not applicable: I have copied the Environment Agency, Ofwat and my MP into this correspondence.] Yours faithfully, [Your name] [Your address] [Your customer reference if you are a Dwr Cymru Welsh Water customer]
This overflow sits in the Rhondda and Ogmore constituency — currently represented by Chris Bryant (Labour). Click below to open WriteToThem with the letter copied to your clipboard — paste it into the message box.
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Subject: Constituent query: storm overflow Hermon Street Treorchy Storm Overflow on the Rhondda Fawr River Dear [your MP, WriteToThem will fill this in], I am writing as your constituent about public storm overflow monitoring data for our area. Environment Agency storm overflow monitoring data for overflow Hermon Street Treorchy Storm Overflow on the Rhondda Fawr River (operator listed as Dwr Cymru Welsh Water) records 38 spill events starting between 17 September 2026 and 17 October 2026; the 32 with a published end time total 3 days. The most recent recorded event started on 16 October 2026 at 03:45 UTC. As of 17 October 2026 at 20:39 UTC, the monitor does not report the overflow as spilling. Further details from the public record: - On the Afon Rhondda, per the OS Open Rivers network (Ordnance Survey, Open Government Licence) - Location: 51.65715, -3.50007 - Sources: Environment Agency National Storm Overflow Hub and Water Quality Archive (Open Government Licence v3.0), cross-referenced via River Truth (https://rivertruth.co.uk/overflow/13652) These figures are taken from public monitoring data as published and may be revised by the publisher. They are not a finding that any permit condition has been breached. [Add your personal context here, for example how you and your family use this stretch of water.] I would like to ask: 1. Whether you support strengthening the regulatory regime for storm overflows, and monitor coverage in particular 2. Whether you would raise the monitoring data for this overflow with the Secretary of State for Environment, Food and Rural Affairs, the Environment Agency or Ofwat Yours sincerely, [Your name] [Your address (WriteToThem requires a postal address to verify your constituency)]
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For active pollution incidents — dead fish, foam, sewage on the riverbank — the EA hotline operates 24/7 and triggers a recorded investigation.