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3 gauges from Grosmont Rhosllwyn River Station to Monnow Gate River Station. None is above its typical high. No storm overflow upstream is discharging now. Gauges in Herefordshire County of, Monmouthshire; levels are checked every 15 minutes.
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| Station | Level now | Status |
|---|---|---|
| Grosmont Rhosllwyn River Station | 0.65 m 17m ago | Within its typical range |
| Skenfrith River Station 9.9 km by river | 0.34 m 17m ago | Within its typical range |
| Monnow Gate River Station 16.0 km by river | 1.97 m 17m ago | Within its typical range |
Stations are listed from source to mouth as the water flows, traced on the river map (OS Open Rivers) and the Environment Agency’s own links between its gauges. A distance “by river” is along the river, and is shown only where the map traces the path.
Contains OS data © Crown copyright and database rights 2026.
Streams and rivers with a gauge whose water joins the Monnow above one of its gauges, from the source down. Named streams without a gauge that have a page here are listed at the end.
Joins the Monnow above Grosmont Rhosllwyn River Station, its highest gauge, no more than 7.5 km by river above Grosmont Rhosllwyn River Station.
| Ewyas Harold | 0.08 m 32m ago | Below its typical range |
Its water passes every gauge on the Monnow, from Grosmont Rhosllwyn River Station down.
Joins the Monnow above Grosmont Rhosllwyn River Station, its highest gauge, no more than 29.3 km by river above Grosmont Rhosllwyn River Station.
| Tafalog River Station | 0.31 m 17m ago | Within its typical range |
Its water passes every gauge on the Monnow, from Grosmont Rhosllwyn River Station down.
Joins the Monnow above Grosmont Rhosllwyn River Station, its highest gauge, no more than 20.8 km by river above Grosmont Rhosllwyn River Station.
| Peterchurch | 0.15 m 47m ago | Below its typical range |
Its water passes every gauge on the Monnow, from Grosmont Rhosllwyn River Station down.
Below Monnow Gate River Station, its water next reaches Redbrook River Station, a gauge on River Wye, 3.1 km by river downstream.
Tributaries and where they join are traced on the river map (OS Open Rivers, edition 2026-04) and the Environment Agency’s links between its gauges. The map holds distances between gauges, not the junctions themselves, so a junction is placed between two gauges, and no further up than the tributary’s own lowest gauge. Contains OS data © Crown copyright and database rights 2026.
5 storm overflows are traced upstream of Monnow Gate River Station, the Monnow’s lowest gauge on the river map: on the Monnow itself, on its gauged tributaries, and on smaller streams that join above there.
Official annual figures for the overflows traced upstream of Monnow Gate River Station, each return added up on its own. The Environment Agency’s return, 2025: 49 spills over 638 hours in total, across the 2 that have a figure. Welsh Water’s own return, 2023: 10 spills over 160 hours, from the 1 that has a figure. 2 of the 5 have no figure for those years. These are two separate returns, so the figures are given side by side, not added together.
Each overflow is listed in the stretch above the first gauge its water reaches, from the source down, as on the Gauges tab. A stretch of the Monnow includes the smaller streams that join it there.
Within 3 km of one of the Monnow’s gauges in a straight line, but the river map cannot say whether their water reaches it.
3 other overflows within 3 km of these gauges are placed below the Monnow’s lowest gauge or on another river, so not listed.
A status is the water company’s own monitor: it says whether an overflow is discharging, never how much or why, and a spill does not by itself explain a change in a river level. A status older than two hours is shown as unknown. Annual figures are the official returns: 12/24-hour spills for England and Wales, overflow events for Scotland (Scottish Water counts differently, so the two cannot be compared). “No data” means the monitor produced no usable data that year, not zero. Overflows are placed on OS Open Rivers (edition 2026-04), which leaves out many small channels: an overflow the map cannot place may still drain here. Contains OS data © Crown copyright and database rights 2026. Sewage in Britain’s rivers →
Live status: © Dŵr Cymru Welsh Water, from its Storm Overflow Map. Annual figures for England: Environment Agency Event Duration Monitoring return, © Environment Agency copyright and/or database right, Open Government Licence v3.0. Annual figures for Wales: Dŵr Cymru Welsh Water’s return to Natural Resources Wales, as compiled by The Rivers Trust, Open Government Licence.
Dated samples taken by the Environment Agency, not live readings. Results are published days to months after the sample is taken, and many points are sampled only a few times a year, or have not been sampled for years.
11 sampling points on the Monnow and the streams that join it above Monnow Gate River Station. 5 have a sample from the last 12 months; 10 have any sample banked. Listed from the source down, grouped by the next gauge each one's water reaches.
| Sampling point | Watercourse (map) | Above the gauge | Last sample | Latest results (river water) |
|---|---|---|---|---|
| Escley Brook, Ponty's Mill | Escley Brook | 23 km | 4 Dec 2024 · 23 months ago | Oxygen 100.8%Temp 6.7 °CpH 8.16Ammonia 0.0036 mg/l |
| Olchon Brook upstream of Longtown | Olchon Brook | 23 km | Last sampled 23 Mar 2017, before the imported period | |
| River Monnow at Llanwonog Farm | Afon Mynwy | 22 km | 3 Mar 2025 · 20 months ago | Oxygen 100.7%Temp 3.5 °CpH 8.13Ammonia below 0.03 mg/l |
| Olchon Brook, Longtown Castle | Olchon Brook | 22 km | 7 Jul 2026 · 4 months ago | Oxygen 101.3%Temp 17.3 °CpH 8.34Ammonia 0.0049 mg/l |
| River Dore at Peterchurch gauging station | River Dore | 21 km | 10 Mar 2026 · 8 months ago | Oxygen 96.8%Temp 9.8 °CpH 7.98Conductivity 440 µS/cm |
| Worm Brook at Lowe Farm Bridge | Worm Brook | 19 km | 14 Apr 2026 · 6 months ago | Oxygen 99.9%Temp 9.3 °CpH 8.21Ammonia below 0.03 mg/l |
| River Monnow at Clodock Mill | Afon Mynwy | 19 km | 28 Mar 2025 · 19 months ago | Oxygen 106.5%Temp 9.7 °CpH 8.27Ammonia below 0.03 mg/l |
| Worm Brook, Killpeck | Worm Brook | 14 km | 8 Dec 2023 · 2.9 years ago | Oxygen 89.9%Temp 7.6 °CpH 7.58Ammonia 0.048 mg/l |
| Jury Brook at Wormbridge Mill | unnamed stream | 10.0 km | 29 May 2026 · 5 months ago | Oxygen 96.8%Temp 15.2 °CpH 8.16Ammonia below 0.03 mg/l |
| CWM Brook at Vedw Farm | Cwm Brook | 9.5 km | 6 Sep 2024 · 2.1 years ago | Oxygen 94.6%Temp 13.9 °CpH 8.12Ammonia 0.0059 mg/l |
| Sampling point | Watercourse (map) | Above the gauge | Last sample | Latest results (river water) |
|---|---|---|---|---|
| River Monnow, Rockfield Park House | Afon Mynwy | 7.5 km | 12 Aug 2026 · 2 months ago | Oxygen 92.4%Temp 18.4 °CpH 8.18Ammonia below 0.03 mg/l |
Distances are along the river to the gauge named. England's samples only.
FloodRadar does not grade these results: there is no overall score, and official river classifications are a separate dataset. A sample taken downstream of an overflow does not by itself show where anything in it came from. River connections and distances are traced on OS Open Rivers (edition 2026-04), which leaves out many small channels.
Water samples: Environment Agency Water Quality Archive, © Environment Agency and/or database right 2026, Open Government Licence v3.0.
Contains OS data © Crown copyright and database rights 2026.
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