Sewage discharge was reported by Cattewater Harbour authority
21:30, 29 Sep 2026Updated 21:30, 29 Sep 2026
Oreston Quay, where the storm overflow drain comes out(Image: Shannon Brown/PlymouthLive)
High tide in Plymouth caused two storm overflows to open along the River Plym.
One overflow at Marsh Mills sewage treatment works and another at Oreston Quay pumping station were reported as ‘active’ on this morning (Sept 29).
It comes a day after Cattewater Harbour Plymouth announced a sewage discharge into the water and warned water sports enthusiasts to avoid using the river for “at least two tide cycles.
The harbour authority said yesterday: “We are aware of a current sewage discharge into the Cattewater.
“If your activities on the river include water sports or other recreational use, we recommend waiting for at least two tidal cycles before heading afloat, as water quality may be temporarily affected.
“Any sightings or concerns relating to pollution should be reported to the Harbour Office, South West Water, and the Environment Agency.”
South West Water has said the release at Oreston was the result of this morning’s spring tide, which happens around the full and new moons and creates a higher-high tide than usual.
The overflow releases at Oreston and Marsh Mills were logged on South West Water’s storm overflow map at around 8am at Oreston Quay, lasting one hour and 40 minutes, and around 8.20am at Marsh Mills lasting three minutes.
At the time of writing, both locations are marked in yellow as ‘this storm overflow has activated in the last 24 hours’.
SWW describes storm overflows as “safety valves” which release excess when the system becomes too full. This is more common in the winter months after bouts of heavy rain.
A South West Water spokesperson said the high spring tide, which was at 8.11am in Plymouth, caused water to enter the sewer and resulted in a short, diluted spill as the tide drained out.
The water company said: “The storm overflow at Oreston Quay was activated this morning as a result of the high tide. The activations are caused by the spring tides entering the sewer and causing a very diluted short spill when the tide drains out. All assets in the area have been checked and are operating as expected.
“We are continuing to look at measures to protect our network, including lining, to help prevent tidal inundation during high spring tides.”
About the Marsh Mills spill, South West Water said: “The storm overflow at Marsh Mills activated this morning as a result of the high tide.
“The activations are caused by the tide entering the sewer and triggering the alarm and there is no evidence of a discharge taking place.”
The water company was today (September 29) fined more than £7.8 million after it pleaded guilty to 18 charges; 17 for illegal water discharge activities and one charge for failing to take reasonable remedial measures following failure at a pumping station.
These took place between January 2015 and July 2021 across Bodmin, Harlyn, Playing Place, Polperro and Plymouth.