The River Cam usually brings to mind idyllic images of students punting beneath the university’s bridges. Yet in its upper reaches, rampant phosphorus pollution has turned the Cam into a slimy, algae-ridden mess.
Campaigners have shared data with i that show elevated phosphorus levels throughout the river, in particular near the outflows of sewage treatment works which are unable to extract the chemical from wastewater.
Phosphorus levels in wastewater come from multiple sources, including human waste, tap water and dozens of household products such as detergents.
Water companies are not required to remove phosphorus at their sewage treatment works unless a specific permit is in place from the Environment Agency. This is not the case with the upper Cam.
Anglian Water, which is responsible for the local treatment works, has said it will install phosphorus treatments in three of them by the end of next year. However, this will still leave three plants discharging high-phosphorus water into the Cam.
High levels of phosphorus have led to excessive algae growth which smothers other plants and deprives the river of oxygen, a process known as eutrophication. This severely depletes the river’s ability to support wildlife.
“What we have is this constant high level [of phosphorus] that is just smothering the river in algae,” said Richard Pavitt, an independent local councillor in Uttlesford, Essex, who has been monitoring the Cam in its upper stretches.
“A chalk stream such as the Cam should have a golden river bed, a gravely river bed with lots of green life in it. Nowhere in this long stretch looks anything like it should do.
“It’s just that there’s no life. There are a few fish, but if I go back 10-15 years, I’ve seen great shoals of fish in the pools and trout and all sorts of things. Now, nothing. It’s all gone. It’s just very, very dead.”
The headwaters of the Cam, which begin in Essex, and its tributaries the Rhee and Granta are chalk streams, a rare and highly ecologically valuable form of river that is almost exclusive to southern England.
They should have crystal clear, cool waters and gravel beds teeming with fish and invertebrates.
Mr Pravitt began taking phosphorus measurements with a handheld device, which showed very high phosphate levels. He had this work verified and replicated by scientists at the Cam Valley Forum voluntary group.
“I’ve been doing this testing with this small handheld device and looking at the results and going ‘This can’t be accurate, this can’t be true’,” he said. Thorough water samples, however, corroborated his findings.
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Phosphorus in rivers can derive from both agricultural runoff and domestic wastewater, but in the case of the upper Cam and its tributaries, the data appears to link it to the latter.
“We saw a marked difference [in phosphorus levels] around several sewage works. So to me that was pretty solid evidence that the sewage treatment works in our catchment are a source of phosphorus,” Dr Mike Foley, a water quality expert at the Cam Valley Forum, told i.
The Granta and the Cam are particularly vulnerable because they are fed by Chalk aquifers which are abstracted by several local water companies to provide drinking water. During the summer, and especially during droughts, it is often the case that the heads of the two rivers dry up.
When this happens, the start of both rivers becomes the outflow pipes of local sewage treatment works.
“In the summer, the head of the Cam is the Newport Sewage Treatment Works effluent pipe. So whatever comes out of the Newport effluent pipe is going down the river as almost 100 per cent of the of the flow,” said Dr Foley.
Newport is one of the sewage works that is set to be upgraded by the end of 2024.
Anglian Water told i: “We are currently developing our investment programme through to 2030 working with the Environment Agency, and will continue to engage with local river groups and others to identify what work is required at other smaller sites in the Cam Valley.”
How phosphorus harms our rivers
Phosphorus is ubiquitous in the British environment and comes from a huge number of sources. Even tap water contains phosphorus, which helps prevent lead from leaching out of pipes.
The two major contributors of phosphorus and soluble phosphates are agricultural runoff, when manure and artificial fertilisers wash off fields during rainfall and end up in streams and rivers, and wastewater. Domestic products such as detergents rely on phosphorus to function, while human waste also has high levels.
While the Environment Agency can set out permissible levels of phosphorus where it deems them to be too high, this is not done by default. It means that most sewage treatment works do not strip it out.
Once it enters a river, phosphorus encourages the rapid growth of algae. In lakes this can often lead to toxic blue-green algal blooms. In rivers, this is more likely to take the form of filamentous algae.
The algae smothers other plants and covers the river bed, which is a particular threat to chalk streams, where the gravel bed is an essential ecological feature that provides resting and spawning grounds for fish.
Most threateningly, the algae uses up the oxygen in the water, leading to eutrophication. This prevents it from supporting other life, killing off plants, fish and invertebrates and starving the animals that eat them.
High phosphorus levels can also encourage the growth of invasive species such as floating pennywort, which can entirely overwhelm a river.
i and our sister title, New Scientist, have launched a joint campaign, Save Britain’s Rivers, to rescue the country’s polluted waters.
Does your river need help? If you have a story, or if you would like i reporters to investigate sewage pumping near you, please email us at i@inews.co.uk.