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Unchecked ‘preventable pollution’ smothering Bristol rivers
Silt from construction sites entering Bristol rivers unchecked, to the detriment of wildlife and ecosystems, has been called a “slap in the face” of volunteers working to clean up the city’s watercourses.
Developers are required by law to prevent runoff which damages rivers. But Bristol24/7 has been told that, due to a lack of enforcement, construction companies operating to the north of the city including Persimmon, Bellway, Barratt and Taylor Wimpey have not acted on the issue which was first raised by the local community in 2021.
Residents and river campaigners looking after the River Trym and Hazel Brook have become increasingly frustrated by the lack of action which is causing the ongoing destruction of biodiversity.
They have reported the pollution incidents to the local authority, South Gloucestershire council, as well as to the Environment Agency on multiple occasions, but say that nothing has changed.
Silt pollution entering the River Trym. The sediment builds up on the bed of the river, smothering habitats and preventing wildlife from eating, resting and breeding. It also alters the shape of water courses and causes flooding as well as having an economic impact – photo: Peter Coleman-Smith
“This pollution…is degrading Bristol’s cherished watercourses and undermining years of community-led restoration downstream along the River Trym,” said Simon Hunter, CEO of Bristol Avon Rivers Trust (BART).
“Dedicated volunteer groups along the Hazel Brook, Trym and Blaise Estate have spent countless hours improving their local river. Their hard work is now being erased by preventable pollution.”
Voluntary groups have been working for more than six years to improve the health of the Trym and its main tributary the Hazel Brook, a Site of Nature Conservation Interest, which flow through Henbury and Blaise Castle Estate and into north west Bristol.
Hundreds of volunteers have cleared out more than 400 tonnes of litter including electric scooters and 18 motorbikes, while more than 1000 hours of volunteer time has been spent pulling up non-native invasive Himalayan Balsam to help reduce silt entering the water.
Alex Dunn and volunteers with the rubbish they pulled out of the Hazel Brook in one clean-up session. Construction companies are re-polluting the river, which is a ‘slap in the face’ after all this hard work, they say – photo: Peter Coleman-Smith
“For the last four years the Environment Agency and local councils have failed to stop silt flowing into the Trym,” said Alex Dunn who leads river health group Trout in the Trym. “If we can’t protect the Trym, how can we expect others to protect bigger rivers?”
Alistair Blackwell, chair of Friends of Blaise, said: “The ponds and brook add hugely to Blaise Castle Estate. Our volunteers have put in a lot of effort to remove silt from them.
“Tonnes of silt have entered the stream, carpeted the bed and almost filled up the entire historic lily pond. This a real slap in the face for them.”
Campaigners are concerned the issue will be exacerbated with the government’s concerted house building efforts.
On behalf of Bristol Avon River Catchment Partnership, a cohort of 16 organisations and groups working to improve water health, chair Richard Cresswell acknowledged the need to build more houses but said: “It is poor that many house builders and developers still seem unable to do this in a way that does not damage the environment.”
The discoloration of the water caused by silt run can be seen clearly at the point where the Hazel Brook joins the River Trym at Combe Dingle – image: Trout in the Trym
Species found in the Avon catchment including otters, brown trout, European eel and water voles are highly sensitive to declines in water quality.
Contaminated construction run-off smothers fish spawning grounds and invertebrate habitats, with knock-on effects for the wider ecosystem as the riverbed gravel and stones required by many species to feed, shelter and breed are covered by sediment.
The build-up of silt can alter the shape of rivers, eventually increasing flood risks, while BART suggests the downstream economic cost of removing the excess silt from locks, harbours and ponds is “significant”.
Resident and Trout in the Trym volunteer Peter Coleman-Smith said that more than 30 sewage pollution reports have been made to Wessex Water which has “done a good job” taking steps to resolve those they are responsible for.
But in comparison, he said, action taken by the building companies has been “laughable” including, at one point, the addition of strawbales to the stream.
Coleman-Smith is keen to stress the concern does not stem from ‘nimbyism’, where residents reject development near their property: “I’ve not heard any of the community group volunteers say there shouldn’t be development here,” he said. “We need more homes – but builders should take basic steps to ensure their work doesn’t trash the environment.”
This ‘outfall’ – the place where a drain empties into a watercourse – was photographed discharging building sediment into the river in November 2025, demonstrating the issue is ongoing – photo: BART
The Environment Agency told Bristol24/7 they are aware of the problem and have increased attendance on site, particularly during rainfall events.
“We have and continue to visit the area regularly, especially after rainfall, and have been taking samples of the discharges and of the brook for evidential purposes,” a spokesperson said.
“Where we have found issues, we have informed housing developers that their current silt mitigation measures for Hazel Brook fall below expected standards, and that they need to undertake urgent action.
“We would expect the situation to improve in the New Year following improvement work by the relevant developers and will take robust enforcement action if needed”.
But the voluntary groups say nothing has changed, and new sites of concern are being identified including silt flowing in to the Longmoor Brook from a construction site in North Somerset.
“Major issues with poorly controlled silt runoff from a building site” flowing into Longmoor Brook was reported on December 21. Campaigners are concerned this is a country-wide issue – photo: BS3 Wildlife Group
“Communities and charities cannot keep being the last line of defence for our rivers,” said Hunter.
“This situation has been allowed to persist for far too long. We are calling for proper enforcement, meaningful intervention and accountability. With large-scale development accelerating across the region, this must be a turning point – not a warning that goes unheeded.”
Main image: BART
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