Gwennap STW SSO Lanner St Day
Storm overflow operated by South West Water. The source names Hicks Mill Stream as the receiving water.
- 141
- Spills in 2025
- 2,673.2
- Recorded hours
- 98.3%
- Monitor operation
- 5
- Years listed
The reported spill count was 15 higher than in 2024. This compares event counts, not discharge volume.
Checking the latest monitor report…
How it compares in 2025
Gwennap STW SSO Lanner St Day recorded 141 spills in 2025. That is more than 99% of the 14,239 overflows in England with a reported figure, and ranks 63rd nationally. Among South West Water overflows it ranks 29th of 1,357; the median South West Water overflow recorded 21 spills. On the Hicks Mill Stream waterbody it ranks 1st of 3.
| Group | Rank by spills | Median spills | Median hours |
|---|---|---|---|
| This outlet | – | 141 | 2,673.2 |
| England | 63rd of 14,239 | 11 | 22.3 |
| South West Water | 29th of 1,357 | 21 | 39.4 |
| Hicks Mill Stream | 1st of 3 | 64 | 38.7 |
Rank 1 has the most spills. Equal counts share a rank. Only overflows with a reported count are ranked. Counts do not measure volume, so a higher rank does not mean more sewage.
Annual spill history
| Year | Spills | Duration | Monitor operation | Source |
|---|---|---|---|---|
| 2025 | 141 | 2,673.2 hours | 98.3% | Official data |
| 2024 | 126 | 2,519.6 hours | 98.8% | Official data |
| 2023 | 158 | 2,972.6 hours | 100% | Official data |
| 2022 | 26 | 50.8 hours | 100% | Official data |
| 2021 | 18 | 23.8 hours | 100% | Official data |
A missing figure means the source did not provide a usable value. A zero is shown as zero. Monitor operation below 90% can make comparison less reliable.
Outlet details
- Water company
- South West Water
- Outlet type
- Storm tank at a wastewater treatment works
- Permit
- NRA-SW-5475
- Activity reference
- A2
- Grid reference
- SW74864044
- Waterbody ID
- GB108048001150Official waterbody record ↗
- Location source
- Official annual grid reference
- Location precision
- About 10 metres
- Location note
- Unknown
About the name and type
The annual return lists this asset as “Storm tank at WwTW”: storm tank at a wastewater treatment works. The overflow comes from storm storage at a treatment works.
The waterbody link opens the Environment Agency record for the exact ID in the return. It is a source lookup; we do not import its classification.
Where it is
The recorded position is about 1.1 km west of the Frogpool reference point in the ONS built-up areas data.
Area and water pages
Check the official record
Public access to this outlet is unknown. Do not enter restricted land or use this page as a route guide.
Open official source ↗Other outlet records nearby
- Gwennap STW So Lanner St DayCurrent status unknown
South West Water · Hicks Mill Stream
- Sparry Ln CSO CarharrickCurrent status unknown
South West Water · Carnon River (S)
- Chacewater STW So ChacewaterCurrent status unknown
South West Water · (S) River Carnon
- Chacewater STW SSO ChacewaterCurrent status unknown
South West Water · (S) River Carnon
Questions about Gwennap STW SSO Lanner St Day
- Who operates Gwennap STW SSO Lanner St Day?
- South West Water is the operator named in the annual record. The permit reference is NRA-SW-5475.
- Where does Gwennap STW SSO Lanner St Day discharge?
- The source names Hicks Mill Stream as the receiving water. This does not show how far a discharge travelled.
- How many times did Gwennap STW SSO Lanner St Day spill in 2025?
- The 2025 return records 141 counted spill events and 2,673.2 hours of recorded discharge. Spills are counted with the 12/24-hour method, so this is not a count of every start signal.
- Can I trust the 2025 figures for this outlet?
- The monitor worked for 98.3% of the reporting period, so the annual figures cover most of the year. They still do not measure discharge volume.
- Is Gwennap STW SSO Lanner St Day discharging right now?
- This record is linked to a company live feed. The panel above shows the latest report we hold, with its date. That report can be old, and the monitor can be offline, so check the date before relying on it. A report that no discharge is taking place is not a water-quality result.
- How accurate is the map marker?
- The marker comes from the grid reference in the official annual return, which is accurate to about 10 metres. It shows the recorded outlet position, not the extent of any discharge.
- What kind of outlet is Gwennap STW SSO Lanner St Day?
- The annual return lists the asset type as “Storm tank at WwTW”, which means storm tank at a wastewater treatment works. The overflow comes from storm storage at a treatment works.
- How does Gwennap STW SSO Lanner St Day compare with other overflows?
- Gwennap STW SSO Lanner St Day recorded 141 spills in 2025. That is more than 99% of the 14,239 overflows in England with a reported figure, and ranks 63rd nationally. Among South West Water overflows it ranks 29th of 1,357; the median South West Water overflow recorded 21 spills. On the Hicks Mill Stream waterbody it ranks 1st of 3. Ranks compare counted spill events only. They do not compare volume or harm.
- Does zero spills mean the water was safe?
- No. A zero means the annual return recorded zero counted spill events for this outlet and year. It is not a water-quality test, and pollution can come from other sources.