Llanberis WwTW Storm Overflow
Storm overflow run by Dwr Cymru Welsh Water, discharging into Afon Y Bala.
"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 28 February (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 Peblic Seiont River Station (Seiont), 13.4 km along the river.
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
4,978 discharge periods since 2 Jan 2020. 4,971 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.
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Thu 1 Oct 2026, 02:0947 min
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Wed 30 Sep 2026, 14:5129 min
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Wed 30 Sep 2026, 07:4448 min
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Wed 30 Sep 2026, 03:581 h 43 min
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Wed 30 Sep 2026, 02:5729 min
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Sun 27 Sep 2026, 13:281 h 26 min
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Wed 23 Sep 2026, 09:513 h 3 min
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Sun 21 Dec 2025, 18:1530 min
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Sun 21 Dec 2025, 10:4515 min
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Sun 21 Dec 2025, 03:0030 min
Show 30 earlier (of 4,978)
| Started (UK time) | Ended | Discharge time |
|---|---|---|
| 20 Dec 2025, 21:30 | 22:00 | 30 min |
| 20 Dec 2025, 18:00 | 18:30 | 30 min |
| 20 Dec 2025, 14:45 | 15:15 | 30 min |
| 20 Dec 2025, 11:45 | 12:30 | 45 min |
| 20 Dec 2025, 09:15 | 10:00 | 45 min |
| 20 Dec 2025, 06:45 | 07:15 | 30 min |
| 20 Dec 2025, 04:00 | 04:30 | 30 min |
| 20 Dec 2025, 01:15 | 02:00 | 45 min |
| 19 Dec 2025, 23:00 | 23:45 | 45 min |
| 19 Dec 2025, 21:00 | 21:45 | 45 min |
| 19 Dec 2025, 19:15 | 20:00 | 45 min |
| 19 Dec 2025, 17:30 | 18:15 | 45 min |
| 19 Dec 2025, 15:45 | 16:30 | 45 min |
| 19 Dec 2025, 14:15 | 14:45 | 30 min |
| 19 Dec 2025, 12:30 | 13:15 | 45 min |
| 19 Dec 2025, 11:00 | 11:45 | 45 min |
| 19 Dec 2025, 09:30 | 10:15 | 45 min |
| 19 Dec 2025, 08:00 | 08:45 | 45 min |
| 19 Dec 2025, 06:30 | 07:15 | 45 min |
| 19 Dec 2025, 05:00 | 05:45 | 45 min |
| 19 Dec 2025, 03:30 | 04:30 | 1 h 0 min |
| 19 Dec 2025, 02:00 | 03:00 | 1 h 0 min |
| 19 Dec 2025, 00:30 | 01:30 | 1 h 0 min |
| 17 Dec 2025, 10:00 | 00:00 | 1 d 13 h |
| 17 Dec 2025, 08:30 | 09:15 | 45 min |
| 17 Dec 2025, 07:00 | 08:00 | 1 h 0 min |
| 17 Dec 2025, 05:00 | 05:30 | 30 min |
| 17 Dec 2025, 02:45 | 03:30 | 45 min |
| 17 Dec 2025, 00:45 | 01:30 | 45 min |
| 16 Dec 2025, 23:00 | 23:30 | 30 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 5,808 raw blocks were merged into 4,978 continuous discharge periods (gaps under 15 min joined).
Rain nearby last 30 days
Nearest live rain gauge: Bethesda Quarry Raingauge, 6.4 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
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.