Cefn Mawr WwTW Storm Overflow
Storm overflow run by Dwr Cymru Welsh Water, discharging into River Dee.
"Not discharging" means the company's monitor reports no discharge right now — not that the water is clean. The feed publishes status only; no discharge volume is measured.
Year by year
Dŵr Cymru Welsh Water's annual Event Duration Monitoring return to Natural Resources Wales (12/24-hour spill count), as compiled by The Rivers Trust. 2026 is our own running count, the same way, from the live feed since 23 September (when we began keeping every discharge it reports) — so it can only be lower than the full year. The official figure is published next spring.
"No data" means the monitor was not working or not required to report that year — not zero.
Downstream of this overflow
The next gauge downstream that the river map places is Manley Hall River Station (Dee), 13.2 km along the river.
Water-sampling points downstream
The nearest Environment Agency sampling points the river map places below Manley Hall River Station. Points between this overflow and that gauge cannot be put in order with it on the map, so they are not listed.
- River Dee at A534 Wrexham Road Bridge, Holt
48 km along the river, below Manley Hall River Station · Last sampled 7 Mar 2025 · 20 months ago - River Dee at Farndon Bridge
49 km along the river · Last sampled 28 Sep 2026 · 26 days ago - River Dee near Eccleston
63 km along the river · Last sampled 28 Sep 2026 · 26 days ago
A sample is dated: it is not the river now, and its results are on its own page. A sample taken after a discharge does not show that the discharge caused what was measured. Samples: Environment Agency Water Quality Archive, © Environment Agency and/or database right 2026, Open Government Licence v3.0.
A river gauge measures the level of the river; it does not measure this overflow's discharge, and a spill does not by itself explain a change there. Traced on OS Open Rivers (edition 2026-04), which leaves out many small channels.
Contains OS data © Crown copyright and database rights 2026.
Discharges we have recorded
957 discharge periods since 8 Jan 2020, 1 still open. 950 of them come from Dwr Cymru Welsh Water's own event-duration-monitoring records (published by the company, Jan 2020 – Dec 2025); the live feed adds anything after that. The official annual count is the figure to quote.
-
ongoing
-
3 h 15 min
-
1 h 30 min
-
3 h 15 min
-
1 h 15 min
-
2 h 45 min
-
45 min
-
30 min
-
30 min
-
4 h 45 min
Show 30 earlier (of 957)
| Started | Ended | Discharge time |
|---|---|---|
| 45 min | ||
| 3 h 0 min | ||
| 15 min | ||
| 30 min | ||
| 1 d 1 h | ||
| 30 min | ||
| 15 min | ||
| 8 h 0 min | ||
| 3 h 15 min | ||
| 2 h 30 min | ||
| 1 h 45 min | ||
| 5 h 0 min | ||
| 1 h 0 min | ||
| 30 min | ||
| 30 min | ||
| 1 h 0 min | ||
| 1 h 15 min | ||
| 45 min | ||
| 6 h 30 min | ||
| 30 min | ||
| 15 min | ||
| 15 min | ||
| 15 min | ||
| 1 d 6 h | ||
| 11 h 15 min | ||
| 30 min | ||
| 30 min | ||
| 4 h 15 min | ||
| 15 min | ||
| 5 h 45 min |
The year figures above use the EA's 12/24-hour counting method, so they are comparable with the official figures; the monitor log's 1,398 raw blocks were merged into 957 continuous discharge periods (gaps under 15 min joined).
What the feed showed
FloodRadar's own record of every change of state Dwr Cymru Welsh Water's live feed has shown for this overflow, kept since : 6 states. The feed publishes its status now and its latest discharge, nothing older; the discharges above are read from this. It is here so the figures can be checked.
Show the last 6 states
| Seen | Status | Since | Latest discharge |
|---|---|---|---|
| Discharging | → no end yet | ||
| Not discharging | → | ||
| Discharging | → no end yet | ||
| Not discharging | → | ||
| Discharging | → no end yet | ||
| Not discharging | → |
Rain nearby last 30 days
Nearest live rain gauge: Five Fords Raingauge, 10.8 km away. Brown shading = when this overflow was discharging; ▼ = a discharge start.
Overflow shading is a timing match, not proof of cause — heavy rain and spills share a trigger. Times come from the water company’s event-duration monitor (site status only; no discharge volume is published).
Where it is
Tell me when this overflow discharges
One message when the company's monitor reports a new discharge here. At most one every 6 hours.
Setting this alert needs JavaScript. The alerts you already have are on your alerts page.
The alert repeats the monitor's status: whether the overflow is discharging, not how much or why. It can only tell you about a discharge that starts after you turn it on.
Concerned about this overflow?
Report pollution you can see or smell to the regulator straight away; the company handles complaints about the overflow itself.
Live status: © Dŵr Cymru Welsh Water, from its Storm Overflow Map. Spill-event history: © Dŵr Cymru Welsh Water's published EDM start/stop records. Annual figures: The Rivers Trust EDM compilation, © Dŵr Cymru/Welsh Water, Open Government Licence. Times are shown in UK local time. FloodRadar republishes the monitor's status; it does not measure discharges itself.