Raw sewage was released into open water in Cornwall more than 10,000 times in 2022, figures show.

Storm overflows normally happen when the sewage system is at risk of being overwhelmed – such as after a heavy rain, or during higher levels of groundwater.

In these cases, water companies may need to release excess water and sewage into rivers and the sea, to prevent water backing up into the streets and people’s homes.

This has an impact on the quality of our natural water sources, with some charities alleging storm overflows are being misused and under-reported.

Figures from the Environment Agency show storm overflows were used 11,285 times within Cornwall’s local authority boundaries in 2022, discharging for a total of around 78,775 hours.

All of these spills were from South West Water’s network.

These figures may not provide a full picture of the amount of water pollution in the area – Cornwall may also be impacted by overspills from areas it shares water sources with. The Rivers Trust said it was particularly concerned by storm overflows being used during hot periods – a risk as England faces a heatwave this week.

Tessa Wardley, director of communications and advocacy at the charity, said: “Discharging untreated sewage in dry weather is bad for both human health and river health – lower river flows mean more concentrated pollutants at a time when more people want to enjoy their rivers. Although a problem in their own right, these discharges are also the ‘canary in the coalmine’ pointing to greater problems in our sewerage and river systems. This could be blockages in the system, groundwater seeping into broken pipes, misconnections, or just poor management choices,” she added.

She urged “robust, urgent action” on sewage and river management to help tackle the climate crisis and threats to biodiversity.

South West Water saw 37,649 overspills across its network in 2022, with 99 per cent of the company’s facilities reporting overspill data last year. In total there were more than 300,000 overspills across England in 2022 – a 19 per cent reduction on more than 370,000 in 2021, although this may have been the product of weather conditions rather than improved infrastructure.

Water minister Rebecca Pow said the amount of sewage pumped into rivers is “utterly unacceptable”, adding the government has a plan to tackle pollution.

She said: “Targets set by the government to reduce storm overflows are very strict and are leading to the largest infrastructure programme in water company history – £56 billion over the next 25 years.

“Shortly, water companies will also publish action plans for every storm overflow in England, something the environment secretary has personally pressed for.”