Cam Valley Forum committee member, Michael Goodhart was pleased to represent Cam Valley Forum in Parliament on 25 February 2026, supporting Pippa Heylings, the MP for South Cambs, as she presented her private members bill campaigning to protect our Chalk streams with UNESCO World Heritage Status
You can read the full text of her inspiring speech here and watch it on YouTube here Note the reference to Cam Valley Forum.
She started her speech by saying:
“I beg to move, that leave be given to bring in a Bill to require the Secretary of State to take the necessary steps to nominate the UK’s chalk streams as a serial UNESCO Natural World Heritage Site.
My Bill concerns a rare natural resource of universal value. We in the UK are custodians of 85% of the world’s chalk streams, our equivalent of the Great Barrier Reef. They are timeless jewels of our natural heritage, yet we are allowing them to be drained dry and to have raw sewage dumped on them by water companies that put profit before people and the planet. My Bill would ensure that we finally give chalk streams the same reverence and protections that we give to our greatest cathedrals or monuments. Our streams and rivers are just as much a part of our national identity and international significance.….”
“…….In my constituency—here with us in the Gallery—there are the Cam Valley Forum, the Cam Catchment Partnership, the friends of the River Shep, the Granta and Fulbourn Fen, and the Cambridgeshire climate and nature forum.“
She finished by saying
“That is why I am joining many voices in calling for the listing of chalk streams, alongside ancient woodland, as irreplaceable habitat, which they certainly are, in the national planning policy framework, in line with the Government’s concession and promise during debate in this Chamber to
“make clear, unambiguously, our expectations for how plan makers and decision makers should treat chalk streams.”—[Official Report, 13 November 2025; Vol. 775, c. 407.]
We should also be ringfencing substantial financing from the water restoration fund.
As a nation that prides itself on its love of nature and is preparing to celebrate the 100th birthday of nature’s greatest advocate, Sir David Attenborough, we have a responsibility to act. It is a global responsibility handed to us by the rocks beneath our feet. Let us embrace it and celebrate it. Let us be the global custodians of our very own equivalent of the Galapagos Islands, the Great Barrier Reef and the rainforest. This Bill would start the journey to secure UNESCO recognition for one of the rarest habitats on Earth. We hold 85% of the world’s chalk streams. With that privilege comes responsibility. Let us rise to it. I commend the Bill to the House.“
How to help the campaign to get Unesco recognition for chalk streams:
The consultation on the National Planning Policy Framework, is available here. Deadline 11:45pm 10 March 2026. Do respond to the consultation, calling for chalk streams, alongside ancient woodland, to be listed as irreplaceable habitat.
If you’d like to help in other ways do get in touch with us via info@camvalleyforum.uk
Do join us for our 2026 AGM and help celebrate our 25th Anniversary. This will be followed by our Guest Speaker, Alison Matthews, Chalk Stream Programme Manager, The Rivers Trust on ‘Finding a way to protect and restore our Chalk Streams‘
Celebration with cake at 7.30pm, to celebrate Cam Valley Forum’s 25th Anniversary
Annual Lecture ~8.00 pm
Annual Lecture: Finding a way to protect and restore our Chalk Streams
Alison Matthews, Chalk Stream Programme Manager at The Rivers Trust will outline the current national policy and legal framework for chalk stream protection and recovery, and share some thoughts about the various government strategies and the challenges.
She will also share some inspiring stories about positive case studies on our chalk streams
About Alison Matthews
Chalk streams have run through Alison’s 30 year career in the environmental sector and so she was delighted to be appointed to manage implementation of the Chalk Stream Restoration Strategy in April 2024. Working for many years in Hampshire as a water resources specialist, Alison understands the pressures facing chalk stream salmon in the iconic Test and Itchen rivers. Working across organisations, she hopes to bring people together to unite them in delivering the ambition of the Rivers Trust to deliver wild, healthy and natural rivers valued by all.
A Portrait of the Cherry Hinton and Coldham’s Brooks
Judging by the interest shown in the CVF 2025 Summer Walk along Coldham’s Brook, readers may be interested in the fascinating ‘portrait’ found on the website of the Friends of the Cherry Hinton and Coldham’s Brooks here
Though the article ranges from the Cherry Hinton Hall vanity project c. 1839 to the unfamiliar activities in 1852 of The Cambridge University and Town Waterworks Co. at Giant’s Grave, and the historical Cherry Hinton Brook channel dredging debacle, not to mention the devastation caused by industrialisation, the Summer Walk followed what must be the very saddest tributary of the Cam, further downstream, the Coldham’s Brook.
It can be conceded that most of its water eventually reaches the Cam but not as a tributary in the conventional sense. It is not a happy state of affairs. To cut to the chase see the six maps in the Appendix.
On 2 December 2025 Mike Foley of Cam Valley Forum’s (CVF) Mike Foley presented a talk on river turbidity and its most probable causes at Newnham Croft Social and Sports Club, to an audience with a wide range of interests.
The slides are available here. They have been edited to provide a little more of the details presented verbally at the talk, and this Blog accompanies the slides from the talk. (It is illustrated with a few of the slides, but we recommend you look at the full set of slides too)
The investigations into turbidity were separate from CVF’s monitoring along the Cam and Rhee of faecal indicator bacteria from 2021 which focused on trying to locate the main sources of the organisms. We now know these enter the river continually in fairly high numbers in the discharged, treated effluent at Haslingfield sewage treatment works, and from other locations.
If you have no time to read further, Mike’s conclusion is that soil in suspension is the most probable reason for the turbidity. Downstream of Wendy into Cambridge, turbidity is further exacerbated by the presence and activities of the non-native, invasive American Signal Crayfish, now present in large numbers. The clayey nature of the soil type along the Rhee is one important factor in this river being far more turbid than others in the Cam Catchment.
We suspected this all along, but for reasons that will unfold, we thought it was necessary to investigate other causes. Past dredging, upstream of Wendy, is implicated.
The history
Turbidity is the formal name for murkiness or cloudiness of water. A former CVF committee member and angler Alan Coulson noted in 2015 that something wasn’t right with the Cam. He photographed the Cam at Hauxton Junction where the Essex Cam, also known as the Granta, joins with the Rhee. The Rhee was very murky whereas the Essex Cam / Granta seemed clear.
In early 2022 while Mike was sampling for faecal bacteria and nutrient levels, he realised that lowering the shiny rake vertically into the water was a simple way to measure “depth to invisibility” (DTI). In other words, he could measure how far down he needed to lower the rake until the head became just invisible. He enthusiastically built up a dataset of DTI from various sites over the year and into 2023. When there were sufficient readings from the Byron’s Pool part of the Cam (actually Brasley Bridge) he sorted the results according to low flow and higher flow conditions. Spookily, at low flows, i.e. low-summer flows, turbidity increased as flow decreased. This did not suggest a specific cause but was a good point to start considering options.
Soon, Mike was using a Secchi tube, extended to 165cm length to capture low turbidity events. He also occasionally used the nephelometer Hanna HI-93703 and the Hanna Multiprobe HI-98594, loaned from Hobson’s Conduit Trust, with thanks to Dr Steve Boreham for maintaining their calibrations.
How turbid are the Rhee and Cam?
Several monitoring excursions in 2025 have clearly shown that the Rhee is clear at its source in Ashwell, but turbidity can reach very high levels in the upper Rhee, peaking around Whitegates Bridge/ Potton to Guilden Morden road/Tadlow (94 FNU at Tadlow on 20 May 2025). Turbidity then reduces downstream. On the same day, Byron’s Pool’s reading was 25 FNU, but still obviously turbid. Turbidity in summer can rise slightly at further sites around the Haslingfield-Harston road bridge. It is then slightly lower at Byron’s Pool, lower still at Sheep’s Green and very low at Clayhithe.
(Note that NFU “Nephelometric Turbidity Unit” and DTI “depth to invisibility” relate to two different ways of measuring turbidity. A large NFU value (as shown in the graph) indicates high turbidity, whereas a large DTI “Depth to invisibility”, as used elsewhere on this website, implies clearer water)
Local farmers around Tadlow recall the Rhee was clear only a few years ago. Photographs taken in October 2012 near Harston reveal the Rhee appeared clear then, in contrast to its high turbidity of the past few years.
Phosphate / sewage pollution
In 2022, WASP (Windrush against Sewage Pollution) reported, “One common feature of the rivers suffering turbidity issues is sewage pollution and a potential link with high phosphate inputs from STWs.” Could these be a major cause of our turbidity? The answer seems to be no.
For instance, the highest turbidity in 2025 was measured along the Rhee near Tadlow where CVF sampling showed that stretch had the lowest phosphate (<0.084 mg/l) of the entire river. Furthermore, CVF monitoring of the Rhee and Cam for phosphate in 2021/2022 from Harston showed no decrease in concentration at the lowest part of the Cam we monitored – Clayhithe (mean of three samples, 0.442 mg/l orthophosphate-P). Yet Clayhithe had the clearest water of the entire Cam.
There exists a particulate whitish chemical called “Struvite” which contains phosphate. This forms when there are equi-molar amounts of ammonium, magnesium and phosphate present – MgNH4PO4.6H20 – and it can form at sewage works. Routinely Mike sampled effluent at several works and using either a Secchi tube or nephelometer, and if struvite was present in sufficient amounts it would show up. One sampling at Haslingfield STW on 30 April 2025 coincided with a storm overflow, and resulted in the following turbidity readings (FNU): (a) treatment using filtration beds, 5.15. (b) treatment using the activated sludge tank, 1.07. (3) pure storm overflow from storm tanks, 7.45. These readings show that the effluent turbidity so far too low to be a contributor, on that occasion. Furthermore, Mike has compiled readings that show effluent at other works can be remarkably clear, though there is usually some small amounts of natural brown particulate matter present, called “floc”, that is part of the treatment process. For instance, Melbourn and Linton STW effluent can be so clear that after filling the entire 165cm long Secchi tube with effluent the Secchi disk at the base of the tube is still visible.
Thus, treated sewage (also the storm overflow above) at the numerous Anglian Water sewage works discharging into the Rhee, Cam or tributaries appear not to contain sufficient particulates to contribute to high river turbidity.
Nor do measurements of the effluent reveal levels of bacteria high enough to cause a turbid “soup”. Also, it’s not in the nature of naturally occurring aquatic true bacteria in a flowing river to form soups sufficiently turbid to explain what we have been seeing.
Algal blooms
Cyanobacteria (blue-green algae) can create turbidity – this has occurred recently at Todd’s Pit at Milton Country Park – but high power microscopical examination of Rhee water show no cyanobacteria in large numbers.
In recognition that the Cam sometimes appears green, a Turner Aquafluor detector of green algal Chlorophyll a was loaned in 2024 from the Zoology Department, Cambridge University. Samples from sites on the Rhee and Cam where the water was grey-brown were found to have zero amounts of Chlor a. No river samples were green.
Suspended soil
Soil appears to be the culprit. It cannot be coincidental that the colour of the arable soils in the upper Rhee and the Rhee banks have some greyish hue in them that matches the colour of the river water in the summer. Mike has passed on samples to Dr Steve Boreham of WildReach.co.uk who confirms that they contain soil. However, it is not all soil – there is also some organic matter and particulate calcium carbonate.
It seems that only small amounts of soil are needed to create turbid conditions. It could be soil resuspended from the river bed, etched out of the bank, or newly arrived via arable ditchworks or directly from fields into the river. The puzzle still to solve is how turbidity in the upper Rhee persists during periods of dry conditions when ditches are dry and there is no runoff from fields. It appears that only small amounts of soil released into the water are needed to make the river turbid.
It seems reasonable to ponder that suspension of extremely fine clay into the water at one point will not persist too far downstream. Perhaps it is only 50m, depending of soil particle size. But if uplift is happening at one point, it will also be happening a little further downstream, but from this second point the soil will be carried a little further on, and so on.
A controversial issue is the dredging of the Rhee to reduce the risk of overtopping during high winter rainfall. Dredging may expose fresh layers of clay that can lift more easily into the water.
American Signal Crayfish
In 2023, Mike saw persistent high turbidity in the Cam during the summer when for weeks there was no appreciable rainfall to drive soil from ditches or arable fields into the river. The tributary Bourn Brook was actually fairly clear compared to the Cam and thus not a major contributor. Some Chalk streams were slightly turbid but not enough to increase turbidity of the Rhee and Cam. In fact, they would be diluting the turbidity
The simple answer to turbidity in dry spells seems to be American Signal Crayfish. This invasive crayfish has been shown markedly to increase turbidity. Populations can be large: over 1600 crayfish of all sizes and age were taken out of a Yorkshire beck headwater just from a 10m stretch. Largely active nocturnally they stir up bed sediment while fighting and feeding, and when capturing and eating juveniles, and tunnel into the bank up to 200cm depth (mostly up to 60cm on the fish pass at Byron’s Pool). The excavations must allow continuous suspension of soil, whilst mature tunnels cause erosion, sometime causing bank collapse.
The Environmental Agency has concluded that that the turbidity of both the Windrush and parts of the Rhee involves the presence of American Signal Crayfish.
Mike has noted increasing turbidity in the Granta and the Essex Cam / Granta at Hauxton Mill. Crayfish are populating more stretches of our rivers (and are common at Hauxton Mill) and as tagging has shown that they can march 100m upstream overnight, he foresees invasion forces moving steadily towards the headwaters. Numbers may be very low at the front of the invasion – however, it has been proposed that only one female and one male need to be present in stretch of 200m if the stream is 5m wide to be the Minimum Viable Population Density, usually undetectable. Over future years we will see more colonisation, and probably therefore even higher turbidity levels where the geological base of the soil in that stretch is of the right type to be suspended.
Conclusions
No evidence that the prolonged turbidity is caused by algal blooms
Not obviously sewage works related
Not a direct phosphate effect
Upper Rhee – probably soil alone
Lower Rhee and Cam – soil + American Signal Crayfish
The geological soil type seems pivotal in determining how turbid the water becomes from soil suspension.
Local farmer perceptions reveal the upper Rhee was not nearly so turbid just a few years ago. Some light dredging in the upper Rhee may be part of the cause.
Actions
Reduce soil runoff from arable fields into ditches or direct into the rivers
Discontinue any dredging of the rivers (when possible)
Reinforce bank sides
Need for scientists to devise a control measure for the crayfish
Trapping of crayfish to reduce populations needs to be thorough and not just removal of adults. A near-impossible task on large stretches of the Rhee and Cam.
Testing of the upper Rhee with environmental-DNA specific to American Signal Crayfish to determine how much of the Rhee around Tadlow it has colonised.
Tuesday 2nd Dec, 6pm Newnham Sports and Social Club, Hardwick Street CB3 9JA
Dr Mike Foley of Cam Valley Forum, has been investigating the water quality of the River Cam for many years. He has been exploring the river from the chalkstream spring head at Ashwell, down to the River Cam at Clayhithe… Along the way, he has been investigating sewage works effluent, phosphates, river flow, the local geology and the surprising impact of the invasive American Signal Crayfish.
He will share the result of his work, attempting to answer questions such as “Why is the river so murky?” “Is aquatic wildlife at risk?” “Is it safe to bathe?” “Can we clean it up?”
The talk is 6pm-7pm at Newnham Sports and Social Club, Hardwick Street CB3 9JA, but do stay for a chat or a drink afterwards.
Comment from Cam Valley Forum on the announcement of the government funding (£179,602.54 from the Water Restoration Fund) for the project “A Collaborative Restoration Plan for the Cam”
Cam Valley Forum welcomes any funding for work to improve the health of the Cam and its tributaries, and congratulates the Wildlife Trust BCN on being awarded these funds. This project is one of 51 across England that have been awarded grants by the Water Restoration Fund (WRF).
The Collaborative Restoration Plan for the Cam consists of three main elements.
A Sediment Study, covering the whole of the Cam, Rhee and Granta
All three elements are led by the Wildlife Trust BCN (although parts of the project are being delivered by other partners, who are getting paid by the Water Restoration Fund via Wildlife Trust). Cam Valley Forum is a founder member of the Cam Catchment Partnership.
The Water Restoration Fundmoney has permitted the appointment of a short-term catchment officer for the Cam Catchment Partnership, who is creating a catchment plan to be published in spring 2026. It also includes two catchment-wide projects, namely Catchment Habitat Opportunity Mapping and a Sediment Study. The mapping will be useful in discussions with landowners and will tie in with the Local Nature Recovery Strategy. The Sediment Study will help us understand where sediment is coming into rivers and how it moves within the catchment, so we can find the best ways to address the excessive amounts of sediment in our rivers. There are also some smaller projects, all of which support the catchment partnership’s aim to empower local people and to ensure that local knowledge informs water resource and river restoration strategy.
About the Water Restoration Fund
However, our rivers need more. Cam Valley Forum, with the Wildlife Trust, has concerns about the governments approach to the Water Restoration Fund. It has been created from the fines imposed on the water companies for the pollution they have caused. Ideally, the water companies should be preventing such pollution occurring in the first place but, if it does happen, they should indeed be paying for the clean-up. In the period 2020 – 2025, these fines amounted to some £850m – a shocking figure in itself. But the £10M being made available in this current round of the Water Restoration Fund is a tiny proportion of that. The grant for the river Cam is helpful, but insufficient to ensure that the activities initiated can remain sustainable. A larger pot (possibly £100M) is promised in the next round of the Water Restoration Fund. However, Cam Valley Forum feels that the government is showing an insufficient sense of urgency to the problems facing our rivers and chalk streams.
Next working Party: Tuesday 30th September 2:30-4:30 Do register here if you’d like to help save Paradise Local Nature Reserve from infestation with the invasive plant, Himalayan Balsam.
We are working in a lovely, very wild meadow in Newnham to which there’s no public access. The elderly “license owner” is losing the battle with the invading Himalayan Balsam, and very much welcomes our help. If allowed to continue spreading, this outgrowth will threaten Paradise Nature Reserve, just downstream
Nell, with one of the “last” Himalayan Balsam plants
A very useful team joined us in small working party on Wedneday 24 Sept to pull up late flowering Himalayan Balsam plants from a private field beside the Cam in Newnham, Cambridge. This outgrowth is threatening Paradise Nature Reserve. We made great progress completely clearing over half the visible infestation in two hours, before the need for tea and cake became overwhelming.
We’re having another working party on Tuesday 30th Sept 2:30-4:30, attempting to finish the job. Do register here if you’d like to help.
If Himalayan Balsam is left, it grows into massive plants, and spreads rapidly, completely overwhelming everything else.
A few days ago, a local resident alerted us to an outgrowth of the invasive weed, Floating Pennywort in the ditch from Fen Ditton to the main river.
With permission from the land owners, we went in with a canoe and removed 25-50kg, putting it in the nettles alongside the meadow, where it can dry and die.
Some years ago, this ditch was completely choked with pennywort….
Pennywort in Fen Ditton Ditch Autumn 2018
…and we cleared it with the help of several working parties.
Sentec orking Party April 2019
But its always important to keep an eye out for regrowth, so 6 months later it was back again….
Regrowth by November 2019
After a few sessions, we got it clear.
However, but its always possible to have missed a little bit, or for new strands to wash in from further upstream. Autumn is the key time to see it, so do keep an eye out for Floating Pennywort in your local rivers and ditches. Please do clear it out if you can safely do so. Once removed, just put it somewhere dry to die, where it won’t blow back into the river. Then we can eradicate this menace from the lower stretch of the River Cam (as we’ve done in the upper Cam)
You can read more about our project to eradicate Floating Pennywort, and see our various advice sheets here
Wealthy colleges, businesses and residents must help to fund repair of the Baits Bite and Jesus Green Locks
As widely publicised both locally and nationally, both Jesus and Bait’s Bite locks are affected by major structural degradation. The locks have been closed to navigation since May 2024. Temporary stabilisation works are due to start at Bait’s Bite, and further surveys of Jesus Lock are necessary to assess the cost of repair. But, as Sunday’s protest, organised by the FUND BRITAIN’S WATERWAYS national campaign which is helping to secure the future of Britain’s inland rivers and canals, made abundantly clear, the situation is urgent.
Boats unable to pass through Baits Bite Lock
Stephen Tomkins of the Cam Valley Forum (CVF) – an organisation dedicated since 2001 to the protection of the Cam and its environment – says:
“With the current emphasis on restoration of chalk streams, many of us would probably prefer a free-flowing river, with a gravel bottom and lush aquatic plant growth, as in the cathedral city of Salisbury. But we are faced with reality. It is often forgotten that Cambridge was once a key inland port, providing access to the North Sea and the Continent via the Cam, Ouse and Wash, and allowing the transport of goods inland, including to the largest medieval fair in Europe on Stourbridge Common”.
The drainage of the fens and the construction of Denver Sluice on the River Great Ouse changed this, reducing river levels as tidal waters were excluded from the Ouse. By the end of the 17th century, both the university and the Corporation of Cambridge were complaining loudly about this. One result was that in 1702, the Conservators of the River Cam were set up under an Act of Parliament to regulate and maintain the river for navigation, which led to the introduction of locks and other infrastructure to help navigation.
With the arrival of the railway, and the development of the road network, the role of the Cam for transporting goods declined. But the economic importance of the Cam to city life has remained. If the Jesus and Baits Bite locks were to fail, the water levels would fall dramatically and fluctuate, in periods of low flow probably providing only a muddy, and at worst, fetid trickle. Punting and rowing would be impossible, the foundations of college walls would be exposed, and the once iconic views would no longer attract selfie-taking tourists.
The root of the problem is that the Conservators, who remain responsible for maintenance of the river, including the stretch between the two locks, has for many years not had the resources it needs. It has no financial support from the City Council, colleges, or University. It depends on its own capital savings and the annual fees paid to it by the owners of river craft, in particular commercial punting. As Clive Brown, a former Conservator states: “The Conservators have suffered for many years from underfunding. The cost of maintaining the river for navigation has to a major extent fallen on those who register their boats, particularly the punting industry. It is high time that the University, and the wider population who benefit from the river, start to bear some of the costs, either directly or through Council subsidies”.
The City Council is offering ‘support’ of various kinds, but CVF feels that much more immediate action is needed. Anne Miller, co-chair of CVF says: “We are deeply disappointed that a city like Cambridge, with some vastly wealthy colleges, global technology companies that generate over £50bn of turnover per year, and millionaire residents, cannot provide the funding needed. The £1.5 million needed for the temporary stabilisation work for each lock island, and the estimated £10-15 million needed for the ultimate replacement of each lock can surely be found.”
As CVF’s River Manifesto[1] puts it: “Are we too busy lecturing other people around the world about ‘saving rain forests’ when our own river is not what it could be? The River Cam, in this University City of world standing, should surely be an example to the world of achieving sustainable development”.
Those who benefit from the Cam, whether directly or indirectly, must dig into their pockets and contribute to its protection.
