I have recently been elected Chairman of the Chiltern Society Rivers and Wetlands Group having been approached for the post, although I was reluctant as I felt it would take over my life, and I was right. However, the Chiltern chalk streams are very special – there are only a few hundred chalk streams in the entire World, and most of them are in Southern England, but in spite of their special nature, they suffer from over-exploitation and need a lot of help. If the term ‘chalk stream’ evokes any image, it should be quite shallow with fast-flowing very clear water. The stream bed is clean shingle and there are strands of water crow-foot trailing in the current which provide cover for numerous aquatic shrimps and other creatures, which are food for brown trout. This is a place beloved of fly fishermen and a perfect spot to enjoy a late spring evening, watching the mayfly dance over the stream.

So on a golden winters day in late November, I took the Metropolitan Line train from Chesham to Rickmansworth, aiming to walk the length of the River Chess (the image above is the Chess in its valley)  from its confluence of with the River Colne upstream to its headwaters at Chesham to discover some of what a Chiltern chalk stream is like today.

I followed a path out of the that followed the railway line a short distance to a footbridge over the river. This was only a short distance from its confluence with the River Colne, whose valley is strewn with flooded gravel pits. The Chess is only about 3 metres in width and shallow enough to clearly see the gravelly riverbed. Scenically, the area isn’t up to much, with the railway on its bank behind and scrubby damp woodland cloaking the banks, but the river is flowing well and free to find its own course. Further down, it skirts a gravel pit before entering the Colne at a major road bridge below Rickmansworth.

Turning upstream, the river is channelled between concrete blanks as it passes under the railway and road, emerging into the light for a short distance before disappearing under the Miller & Carter Steakhouse. Their building was one of several working water mills in the area and the mill race still runs underneath the restaurant. The stretch between the Colne and the M25 is very built up, with the sprawl of Rickmansworth, Croxley Green and Loudwater crowing in upon it. However, upstream of the restaurant, the river has its way for about a mile, apart from a few old weirs, winding between reed beds and marshy scrubland where wildlife has its way. Following the footpath just to the north of it, there is a stark contrast between the rigidly manicured arable fields which rise up the chalk hillsides and the very scruffy, but biologically diverse, riverbanks where herons, wildfowl and foxes hide.

After a kilometre, there is a foot bridge over the river where, in a side channel, a pair of moorhens are browsing among the watercress: the place feels quite remote but is, in reality, a green island among suburban sprawl.

The Chess Valley Walk then leaves the river and is, sadly, constricted between high wire fences as it skirts a dense woodland through which the river passes: the fence is pointless on the woodland side as it is too dense to enter. The path emerges onto an open marshy area that is dense with dried with the stalks of summer grasses and flowers with Loudwater Farmhouse visible among the trees in the distance. The river itself looks quite natural at this point, gently flowing between reedy banks with open meadows beyond.

At Loudwater, the urban sprawl crowds in on the river, and in one private estate its banks are peoples’ gardens, so that where you can see it, the river looks dark and crowded in by overgrowing vegetation and buildings. This would be prevented by building regulations these days for the sake of wildlife and flood prevention. Emerging from Loudwater, the river meanders the short distance to the M25 through a mixture of woodland and business premises before disappearing into another culvert under the motorway.





Once the motorway is crossed, the river valley opens out and the Chess is relatively free of concrete and buildings all the way to Chesham, so at last it begins to reveal more of the charm of a chalk stream. Initially the area is wooded where Chorleywood Park extends down to the river, and a lone house which is called ‘The Fisheries’ stands secluded among the trees. The river water runs clear on a gravelly bed, albeit along with the odd bit of rubbish that someone dropped, careless of its destination.

The Chess Way crosses the river to the north bank at a point where it widens to form a shallow pond and crosses a small bog on a boardwalk. From the Sarratt Mill to where the river turns towards the west at Mount Wood is a delightful and interesting stretch of river that lies under the village of Sarratt, perched on its hill nearly 200 feet above. I spot a kingfisher perched on a branch over the stream then, a little further on, a heron standing dead still on a small weir and too hidden by the trees to photograph: these wooded stretches are difficult to access, leaving wildlife to its own devices.

The countryside opens out onto grassy fields on both banks, the river reflecting the sky as it glides gently past browsing cattle. A moorhen emerges from the reeds briefly as I pass a woman doing slow exercises in the sun: focused and silent. Then, a little further on, the fields are replaced by reedy marshes once more and the stream is free to wander at will.


Just after Moor Lane, I am surprised to see a group of lamas browsing by a pond: this is Crestyl Watercress which is the only remaining active watercress farm on the Chess. Sadly it is closed, still suffering the after-effects of the hot, dry 2018 summer which deprived it of water. Apparently what water there was in the river became contaminated with sewage following an accidental release and the combination of circumstances killed the crop. All chalk streams are likely to suffer in a drought as their natural flow comes from springs which depend upon the water table being sufficiently high. These days, the Chess also receives much of its flow from the sewage works on its banks which, when operating well, emit water that is almost drinkable. However, if there is an accidental release of untreated sewage, it has a severe effect on the small rivers like the Chess.  With increasing populations in the area and high demands for water, protecting the Chiltern chalk streams takes a great deal of care and effort on the part of the water companies; so land owners and local communities must play their part if the rivers and their wildlife are to be kept in good condition.

Soon after, the river bends south and leaves the footpath, which skirts the Frogmore Meadows Nature Reserve, a rare lowland meadow managed by Herts and Middlesex Wildlife Trust. The main attraction and purpose is the wildflowers, which attract a wide range of insects in the spring and summer. However, even on this winter’s day I encounter a green woodpecker, reed buntings, a little egret, and a kestrel within twenty minutes. Sadly none were in the mood for posing for a portrait. The water is running clear and fast in the river, and watercress flourishes on the stream edges where reeds have not taken over.

The river and footpath come together once more at Chenies Mill Farm, where I meet a young lady who has nets, jars and notebooks. She is a student at Southampton University who is studying the Chess for her dissertation and is monitoring this part of the River. She tests for river fly, phosphate, nitrate and oxygen saturation and allows me to photograph the contents of one of her jars.


The larger orange-tinged creature on the left is a mayfly nymph ( Ephemera Danica), which is one of the river fly larvae that indicates a healthy stream. The grey creatures on the right are Gammarus water shrimps which are native and found in most healthy British streams. Less welcome crustaceans, and much larger, are the American Signal Crayfish, which are more aggressive than our native white-clawed crayfish and have replaced them in most British waterways, where they breed very successfully. There seem to be a lot of them in the Chess.

It is a very heartening to know that young people are interested in our rivers and streams and that this sort of work is going on as the condition of waterways throughout the country is less good than it should be, with most of the classed as being in moderate or poor condition by the Environment Agency. The clarity of the water and number of crustaceans suggests that the river has recovered well since the summer drought and pollution problems, but it is unlikely that the water is as pure as a chalk stream can be when it emerges in spring.


There follows another stretch of reed marsh that is replaced by wide grassy pastures with lovely views along the river and over the valley to wooded hills. Approaching Latimer, the scenery is rather spoiled by barbed-wire fences along and across the river, but the stream flows well over its clean gravel bed. A small shallow stream joins the Chess here which is very full of Canadian pondweed, duckweed and other vegetation, all of which suggests high dissolved nutrients. A really healthy chalk stream is high in calcium, but low in nitrates and phosphates, limiting the growth of vegetation. However, the fact that there is water in it may be a good sign, indicating that the underground water table is at a good high level.


As you cross the road that descends the hill from Latimer, the river changes abruptly to something quite different which will be explored in part 2 where the tour continues to the headwaters of the Chess in Chesham Town.






  1. This is fair summary. The generic problem for the Chiltern Chalk streams is the amount of water taken by boreholes for water supplies. Affinity do not have any reservoirs, the company has an abstraction point from the Thames at Bray and an expensive facility for using Grafham but basically they have to use boreholes. The situation is unlikely to improve. I shall be interested to read where the highest point on the Chess where there is water. I believe you will not find any above Chesham Town Centre.

    On a minor point the Scots Bridge Mill is actually the original Mill building. There were others in Loudwater and Solesbridge. They used to produce paper for the Illustrated London News until they were closed down because of the pollution that they caused.

  2. Thanks Hugh. There is a slight flow of water below the roundabout in Chesham, but not in the so-called ‘water gardens’ immediately above. Then there is the problem of Vale Brook which brings down a lot of nasty run-off during heavy rain. Not simple and we have quite a fight on our hands to turn things around. Doug

  3. After several visits recently, coming through Sarratt to Chorleywood, the river is amazing in its apparent purity and it is certainly a local place to be treasured, we were stunned to find crayfish when basically looking for minnows but many of the butterflies appeared unusual too, especially a blue and white variety.We noted the bullhead fish too but wondered if frogs and toads were native as well.When is the best time to observe Kingfishers please?

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