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Looks can be deceiving when it comes to the state of UK rivers. I recently spent some time by the Fal river in south-west England, which looks beautiful and pristine, but is far from it. Much of it is in the Cornwall Area of Outstanding Natural Beauty and the river is the source of the Fal oyster, a protected designation of origin food. Yet it has been dubbed “the most polluted river in England”.

Last year, analysed Environment Agency (EA) data on sewage spills in England and found that the Fal is the most fouled river in the country. In 2021, raw sewage flowed into the river for nearly 7500 hours, or more than 10 solid months, from one or more of the 103 storm overflows that discharge into it.

That seems shocking, but such events are an inbuilt feature of the wastewater treatment system in the area. They happen after heavy rain – not uncommon in these parts – meets Cornwall’s 100-year-old drains. This is a combined system that mixes sewage (brown water) and household drainage (grey water) with rainwater and sends all of it to treatment plants.

“It’s archaic,” says at The Rivers Trust, a conservation charity based in Callington, Cornwall. “It hasn’t been updated and upgraded. Sewage leaves your house in a pipe and it then goes into a pipe that the road drains go into as well.”

After a storm, this deluge of rainwater and sewage overwhelms the treatment plants, threatening backflow of dirty water into homes and businesses. The local water company, South West Water, is permitted to open the emergency overflow pipes and discharge the excess straight into the Fal. “It’s a massive problem,” says Wardley.

One way, then, to gauge the likely health of a local river is to find out whether your sewage system is combined with rainwater run-off or is separate. In general, urban areas combine their sewage and rainwater while rural ones keep them separate. But this is only a rule of thumb, as Cornwall’s system shows.

Alternatively, the EA publishes . Similar resources exist for the other nations of the UK. It takes a bit of digging, but the information is there in granular detail. I was able to find that an overflow pipe near my accommodation in Cornwall, which drains into the Fal from a wastewater treatment plant in Mylor Bridge, made 179 discharges in 2021, adding up to 145.8 hours.

But bear in mind that this is far from comprehensive data, as not all of the overflow sites are monitored. Only 67 of the 103 discharging into the Fal collect data.

There are other gaps in the record too. The data only records the number of discharges and their duration, not the quantity of sewage-infused water going in. To the naked eye, the Fal clearly isn’t awash with sewage, and the Independent’s story provoked fury in nearby communities. The claim that the Fal is the most polluted in England is “absolute rubbish”, oyster fishery owner Martin Laity at Sailors Creek Shellfish, in the village of Flushing,

at the Westcountry Rivers Trust said the story was “dismaying”. “This isn’t about the River Fal being the most polluted in the UK but rather the river suffering from the longest duration of a Combined Sewage Overflow (storm drains) spilling,” he told The Packet. The monitoring that water companies do “only shows frequency and length of spills but crucially not volume,” he said. In other words, the Fal is the river most frequently polluted with sewage in England, but not necessarily the most polluted.

Status updates

To get a better idea of the state of a river in the UK, you can check its ecological and chemical status. All surface water bodies in the country are assessed according to criteria laid down in the European Union’s Water Framework Directive, and the classifications are published by the EA in England and its counterparts in Scotland, Wales and Northern Ireland.

These ratings indicate that you can pretty much guarantee that any river in the UK isn’t in the best ecological health and is polluted with chemicals.

On ecological health, there are five categories ranging from high to bad. , which advises the UK government and devolved administrations, show that none of England, Wales and Northern Ireland’s rivers is in the highest category, and only 8 per cent of Scotland’s rivers reach this standard.

On chemical pollution, rivers are either classed as good or failing, based on allowable concentrations of 52 priority substances. According to these assessments, every single one of England’s rivers is failing.

“It’s really becoming apparent that, actually, the chemical state of rivers is really, really poor,” says Wardley. The list of pollutants and their sources is long: pesticides, fertilisers, “forever chemicals” such as per- and polyfluoroalkyl substances (PFASs), factory effluent, microplastics, microfibres, medications that have been flushed down the toilet, paint thinners and cooking oil chucked down the drain, detergents, car wax and so on.

Without a chemical testing kit, however, there aren’t many obvious signs of these pollutants. But there are visual clues that are decent indicators of the state of a river, in a more general sense, wherever you are in the world.

“You can look at the appearance of the river in terms of its physical nature,” says at CREW, Scotland’s Centre of Expertise for Waters at the James Hutton Institute in Aberdeen. “Is it straight? Is it canalised? Is it deep? Is it not connected to its floodplain? These are all unnatural attributes.”

Natural attributes are easy to spot, says at the UK Centre for Ecology & Hydrology in Wallingford. “Natural rivers have complicated forms, meanders and so on, and habitat diversity. There’ll be one bit that’ll be deep and the next bit is quite shallow, and you can see some rocks and you can see the water being turbulent and sparkling a bit, and you can often hear it. All those things you note from a healthy river that you don’t get if you go to an unhealthy river.”

As for water quality, it is difficult to judge from simply looking at the water itself. “Rivers are often quite murky and people will think, ‘I wouldn’t jump in there’, but very often that’s just sediment,” says Wardley. “They collect colour from their geology, so they’re not necessarily polluted, but really you can only tell if you start to look at the plants and animals.”

Smaller species are a good starting point. “In terms of water quality, there could be issues such as very high algae cover, or even, in extreme cases, blue-green algae, which is dangerous,” says Addy.

Flagship species

Wardley says a total giveaway is the presence of so-called sewage fungus, a gross-looking mass of slimy, brown filamentous bacteria that thrive in nutrient-polluted water. “If you see that coating the stones and in the water on the river, you can be pretty sure you’ve got water quality issues.”

Larger flora and fauna are good indicators of river health. The presence of fish is a positive sign, as is lush, green vegetation in the channel and along the banks. There are also a few “flagship species” of good health, including otters, freshwater pearl mussels and birds called dippers. “They rely on a good supply of macroinvertebrates in the river and they’re an indicator of good water quality,” says Addy. As for raw sewage, we all know it when we see it.

“It can be quite hard to tell just by looking at the river,” says Wardley. “But there are signs that anyone can see. And smell.”