It has been widely reported that our rivers are polluted, with not a single river in England in good overall health. What isn’t so well known is that a major source of this pollution comes from our roads – oil spills, particulate matter, and microplastics from tyre and brake wear. Every time it rains, this toxic brew gets flushed into streams and rivers.
National Highways, which manages the strategic road network (SRN), is responsible for 18,083 outfalls (pipes) that go straight into watercourses (channels through which water flows including rivers, streams, drains or culverts) and 7,700 soakaways that go into the ground. In 2023 it revealed that a total of 1,236 of its outfalls and soakaways had “a potential high risk of pollution”1.
Although it should be a top priority for National Highways to ensure that as little pollution as possible gets into our watercourses and valuable wildlife habitats, its current plan focuses only on “high risk outfalls”. It was pledging to “mitigate” these by 2030, although that date now appears to have slipped, funding has not materialised, and the pollution continues.
How bad is the problem?
A 2024 report from Stormwater Shepherds revealed that astonishingly neither the Environment Agency nor National Highways routinely monitor runoff from the SRN as National Highways relies on its own risk assessment tool2. It also found that pollution from sites that National Highways does not monitor, on the basis that they are “low risk”, can in reality be very high.
National Highways 2030 Water Quality Plan, published in 2023, found that 1,236 outfalls and soakaways on the SRN had a “potential high risk of pollution”. So the problem could be much higher than thought if the risk has been underestimated.
Analysis by The Guardian and Watershed Investigations revealed that about 70 verified or potential high risk sites are located in our most precious water habitats such as Special Areas of Conservation (SAC) or Sites of Special Scientific Interest (SSSI), with another 250 or so within 1km (0.6 miles) of a legally protected wildlife site3. The Guardian reported that these included chalk rivers such as the Kennet and the Itchen.
What is being done about it?
Despite the seriousness of the situation, it appears little is being done beyond making and breaking woefully unambitious targets. They are effectively kicking the can down the road. Meanwhile, scarce funds are being diverted away from tackling the problem and into more roadbuilding. The 2023 Water Quality Plan set out “a high-level programme of work that achieves the plan to mitigate all high risk outfalls by 2030” but stressed that this will be subject to funding.
The Plan revealed that just four outfalls had confirmed funding and committed delivery in 2023-24, with a further 17 identified for “potential” delivery in 2024-25.
However, National Highways’ 2023-24 Annual Report says it delivered just two “water quality” initiatives during the year, while its 2024-25 Annual Report4 says it delivered mitigations to only four high risk outfalls, and just three high priority soakaways.
The Water Quality Plan stated that, by the end of the second Road Investment Strategy (RIS2) in March 2025, National Highways would confirm its understanding of high risk pollution sites and produce a delivery plan for RIS3 to tackle them.
However, the new government put back RIS3 by a year and the company’s “interim settlement” for 2025-26 prevaricates further by only promising to develop a programme of water outfall mitigations, and deliver works only “where appropriate”. The recently published draft RIS35 made only a fleeting reference to reducing water pollution.
National Highways’ 2025 Annual Report repeated that “1,236 high priority drainage assets were validated and verified”, despite these already having been identified two years prior in the 2023 Water Quality Plan. However in August 2025 National Highways said it was still finalising the data. It said it expects to rectify between 180 to 200 outfalls and soakaways.
National Highways is currently treading water, but with no funding and no plan to deliver much needed mitigation, it could find itself up a highly polluted creek without a paddle.
What does the law say?
Stormwater Shepherds pointed out that while Section 100 of the Highways Act 1980 allows highway authorities like National Highways to discharge surface water into any inland or tidal waters, a discharge of polluting matter into a watercourse would usually require a permit from the Environment Agency under the Environmental Permitting Regulations 20166.
The group argues that highway authorities are not exempt from enforcement action and that the Environment Agency should uphold the requirements of EU directives like the Environmental Quality Standards Directive, including controlling any highway discharges that prevent compliance with these standards.
Case Study: M25
More than 200,000 vehicles use the M25 every day – around 15% of all motorway traffic in the UK – but, despite this, National Highways is neglecting to maintain it properly.
In 2024 New Civil Engineer reported, based on a freedom of information request, that runoff ponds for water and pollution management around the M25 could be full of hazardous waste as National Highways was unable to identify when they were last cleaned7.
The magazine explained that runoff ponds help with water management and prevent flooding but must be cleaned regularly because pollutants in the runoff could enter the wider catchment.
But National Highways was only able to provide maintenance dates for seven of the 94 runoff ponds around the M25 for which it is responsible.
Case study: M27
There have been very serious longstanding issues with toxic outfall from the M27 draining into the River Hamble, part of the Solent Maritime Special Area of Conservation (our highest category habitat). Hampshire County Council and the River Hamble Harbour Board have lobbied National Highways for years to fix this but the company has repeatedly broken promises to address the issue.
It had a golden opportunity when it converted this stretch of the M27 into a “Smart Motorway”, with works beginning in 2018. It initially planned a two-phase approach to the threat, with the first phase amending outfall pipes to discharge onto the foreshore, with a possible second phase involving a pollution control system.
The scheme was promised funding under the Environment Designated Fund under the 2015-20 Road Investment Strategy but in 2020 Highways England (as it was then called) said the cash had been returned to the central pot as the cost was too high.
In January 2022 the chairman of the River Hamble Harbour Board, Hampshire county councillor Sean Woodward, told Highways magazine: “It’s an ecological disaster waiting to happen. We have to prepare a drainage system to ensure this doesn’t happen, and we need to do that sooner rather than later.8”
Two months later, roads minister Baroness Vere told Cllr Woodward: “National Highways’ Designated Funds programme has a scheme for the Hamble Bridge planned for feasibility in 2022/23, design in 2023/24 and construction in 2024/25, subject to securing approval of funding for each stage.9”
However, the “drainage feasibility study” appears to have been tied to a wider rehabilitation plan for the bridge, which also does not have confirmed funding10. As of 2025, many years after National Highways first promised to act, nothing has been done with pollution from the M27 pouring daily straight into the River Hamble.
What’s the solution?
Stormwater Shepherds has pointed out that there is no shortage of treatment technologies and devices for managing highway runoff; what is missing is the will – and the funding – to implement them. National Highways has Designated Funds exactly for this sort of purpose. However, as we have previously reported, these funds have been syphoned off for projects not related to the Strategic Roads Network (such as dance classes and school play equipment) to buy local support for controversial road projects like the Lower Thames Crossing. This has left a gap in funding to tackle critical issues like National Highways’ persistent polluting of water courses.
However, using Designated Funds to tackle road runoff risks treating this as a “nice to have” rather than a core part of its activities, and would see the issue competing with other environmental imperatives, such as increasing biodiversity. Tackling road runoff should be given higher priority and treated as core work by National Highways, funded out of their main RIS3 budget. Instead, mega-road projects like the £16bn Lower Thames Crossing and the £2.2bn A66 will swallow up most of the RIS3 funds, leaving protecting our water courses low down the list of funding priorities.
Whichever budget the funding comes from, it will need to be substantial for the company to finally get on top of the serious damage runoff from its roads is doing to our natural environment.
Stormwater Shepherds also said that the National Highways water risk assessment tool has reported hundreds of outfalls that potentially pose a high risk of pollution. It argued that on this basis the Environment Agency should serve notice on the company to apply for a permit.
Take Action
Write to your MP today to tell them this is unacceptable and to ask them to contact the Transport Secretary about this issue.
- National Highways 2030 Water Quality Plan, National Highways, August 2023 ↩︎
- Bold, new report on pollution from highway runoff to raise awareness of the problem and possible solutions – Stormwater Shepherds ↩︎
- Hundreds of potentially toxic road runoff outfalls polluting England’s rivers, The Guardian, 5 October 2023 ↩︎
- Keeping our major roads running all year round, Annual report and accounts 2025, National Highways, July 2025 ↩︎
- Draft Road Investment Strategy 3, DfT, August 2025 ↩︎
- The Environmental Permitting (England and Wales) Regulations 2016 ↩︎
- M25 runoff ponds possibly full of hazardous waste due to National Highways ‘avoiding liabilities’ | New Civil Engineer ↩︎
- Highways Magazine – No money to protect river facing ‘ecological disaster’ after £250m works ↩︎
- M27 bridge work over River Hamble to prevent ‘ecological disaster’ in Hampshire will go ahead – but won’t be completed until 2025 ↩︎
- https://democracy.hants.gov.uk/documents/s124693/Environmental%20Update.pdf ↩︎
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