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Live levels from 5 monitoring stations across Hertfordshire, Surrey, updated every 15 minutes.
| Station | Level now | Status | ||
|---|---|---|---|---|
| Knowle Green | 0.70 mASD 1h ago | Well above high | ||
| not connected on the river map | ||||
| Furneux Pelham | 0.04 mASD 1h ago | Low | ||
| 6.4 km by river | ||||
| Little Hadham | 0.03 mASD 1h ago | Normal | ||
| 12.2 km by river | ||||
| Mardock | 0.11 mASD 1h ago | Normal | ||
| Station | Level now | Status |
|---|---|---|
| Staines Ashstructure | 0.07 mASD 1h ago | Normal |
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 Ash above one of its gauges, from the source down. The river map knows where gauges are, not every stream, so a tributary without a gauge is not listed here.
No gauged tributary joins the Ash above Mardock on the river map. Streams without a gauge are not counted here.
Below Mardock, its water next reaches Hoddesdon, Rye Bridge, a gauge on River Lee, 8.1 km by river downstream.
No gauged tributary joins the Ash above Knowle Green on the river map. Streams without a gauge are not counted here.
Below Knowle Green, its water next reaches Molesey Lock, a gauge on River Thames, 15.1 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.
2 storm overflows are traced upstream of Mardock, the Ash’s lowest gauge on the river map: on the Ash itself, on its gauged tributaries, and on smaller streams that join above there.
Official figures for 2025, for the overflows traced upstream of Mardock: 15 spills over 117 hours in total, across all 2.
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 Ash includes the smaller streams that join it there.
None of the storm overflows FloodRadar holds is traced upstream of Knowle Green on the river map. That is not the same as none: the map leaves out many small streams and culverts, so an overflow it cannot place may still drain here, and not every company publishes every overflow.
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: © Thames Water storm overflow activity data, licensed under CC BY 4.0. Annual figures for England: Environment Agency Event Duration Monitoring return, © Environment Agency copyright and/or database right, Open Government Licence v3.0.
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.
2 sampling points on the River Ash and the streams that join it above Mardock, and below it. 2 have a sample from the last 12 months; 2 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) |
|---|---|---|---|---|
| Ash at Bridge North of Widford | River Ash | 4.9 km | 21 Sep 2026 · 17 days ago | Oxygen 94.3%Temp 12.5 °CpH 7.9Ammonia below 0.03 mg/l |
| Sampling point | Watercourse (map) | Below the gauge | Last sample | Latest results (river water) |
|---|---|---|---|---|
| Ash at Easneye | River Ash | 3.9 km | 1 Sep 2026 · 37 days ago | Oxygen 79.6%Temp 14.5 °CpH 7.86Ammonia below 0.03 mg/l |
2 sampling points on the River Ash and the streams that join it above Knowle Green, and below it. 2 have a sample from the last 12 months; 2 have any sample banked. Listed from the source down, grouped by the next gauge each one's water reaches.
| Sampling point | Watercourse (map) | Below the gauge | Last sample | Latest results (river water) |
|---|---|---|---|---|
| Ash above Ashford Common Waterworks | River Ash | 6.5 km | 21 Sep 2026 · 17 days ago | Oxygen 57.3%Temp 14.2 °CpH 7.63Ammonia below 0.03 mg/l |
| Ash above Thames | River Ash | 8.7 km | 21 Sep 2026 · 17 days ago | Oxygen 81.7%Temp 16.7 °CpH 7.9Ammonia 0.031 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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