Thames Water · overflow TWL00037
No active event
Recorded by the operator as Grand Union Canal. The outfall is 13 m from the River Bulbourne on the Ordnance Survey river network, which is the river this page groups it under.
The monitor for overflow TWL00037 (operator listed as Thames Water) reports no current spill. The data records no discharge events in the last 30 days.
📍 51.75079°, -0.53394°
6 other overflows discharge into the Grand Union Canal. Combined recorded discharge in the last 30 days: 4h. Operated by 2 different water companies.
No spill events recorded in the last 30 days.
What the water company itself reported to the Environment Agency’s annual returns for this overflow, year by year. 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 |
|---|---|---|---|---|
| 2024 | 157 | 1,776h | 100% | hub id |
| 2025 | 35 | 210h | 100% | hub id |
2024, the operator's stated reason: "Data collection - Confirmed exceptional weather"
2025, the operator's stated reason: "Performance - Asset configuration (e.g. PS/rising main/storm tanks)"
Source: Environment Agency, Event Duration Monitoring storm overflow annual returns, all years. Matched to this overflow by hub id.
The nearest Environment Agency rain gauge, Chenies, is 6.8 km from this overflow. It recorded 1.0 mm in the last 48 hours.
| Day (UTC) | Rain |
|---|---|
| 18 Oct 2026 | 0.0 mm |
| 17 Oct 2026 | 0.0 mm |
| 16 Oct 2026 | 3.4 mm |
| 15 Oct 2026 | 0.0 mm |
| 14 Oct 2026 | 0.4 mm |
| 13 Oct 2026 | 1.8 mm |
| 12 Oct 2026 | 1.6 mm |
Rainfall comes from 15-minute Environment Agency readings rolled into hourly and daily totals; the 48-hour figure rests on 183 of 192 possible readings. The gauge is 6.8 km from this overflow, so it may not match the rain at the site itself, and the latest day may be incomplete. Rain figures do not show whether a discharge was permitted; that is a matter for the regulator. How we keep the record.
Latest readings at the Environment Agency gauge "Old Fishery Lane", on the River Bulbourne, which is 2.7 km from this overflow.
These are the Environment Agency's own gauge readings at the named station, shown for context. The station measures the river, not this overflow, and a reading does not show whether a discharge occurred or was permitted. Trend compares the latest reading with the one nearest 24 hours earlier; a change of 5% or less is shown as steady. How we keep the record.
TH-PCNR0047 · FRESHWATER - RIVERS
1.4 km away · last tested 13 weeks ago
TH-PCNR0191 · FRESHWATER - RIVERS
1.9 km away
No swimmer-relevant measurements available.
TH-RTN0003 · FRESHWATER - RIVERS
2.7 km away
No swimmer-relevant measurements available.
TH-RSN1770 · FRESHWATER - RIVERS
3.1 km away · last tested 4 weeks ago
TH-PCNR0004 · FRESHWATER - RIVERS
4.2 km away · last tested 3 weeks ago
TH-PCNR0059 · FRESHWATER - RIVERS
4.5 km away · last tested 6 weeks ago
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 TWL00037 on the Grand Union Canal: request for information Dear Thames Water, I am writing about storm overflow TWL00037 on the Grand Union Canal. Environment Agency storm overflow monitoring data for overflow TWL00037 on the Grand Union Canal (operator listed as Thames Water) records no spill events starting between 18 September 2026 and 18 October 2026. As of 18 October 2026 at 06:56 UTC, the monitor does not report the overflow as spilling. Further details from the public record: - On the River Bulbourne, per the OS Open Rivers network (Ordnance Survey, Open Government Licence) - Location: 51.75079, -0.53394 - 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/3912) 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 work, if any, is planned at this overflow, and on what timeline 3. 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 Thames Water customer]
This overflow sits in the Harpenden and Berkhamsted constituency — currently represented by Victoria Collins (Liberal Democrat). 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 TWL00037 on the Grand Union Canal 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 TWL00037 on the Grand Union Canal (operator listed as Thames Water) records no spill events starting between 18 September 2026 and 18 October 2026. As of 18 October 2026 at 06:56 UTC, the monitor does not report the overflow as spilling. Further details from the public record: - On the River Bulbourne, per the OS Open Rivers network (Ordnance Survey, Open Government Licence) - Location: 51.75079, -0.53394 - 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/3912) 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)]
MP details are looked up live from the UK Parliament Members API under the Open Parliament Licence v3.0. River Truth makes no claim about this MP's voting or advocacy record on water issues — they are shown solely as the elected representative for this constituency.
For active pollution incidents — dead fish, foam, sewage on the riverbank — the EA hotline operates 24/7 and triggers a recorded investigation.