Upper Thames Fisheries Consultative committee WQR0019
Written evidence submitted by Richard Knowles, of the Upper Thames Fisheries Consultative committee (UTFC)
Since its formation in the 1970s the UTFC has represented the interests of angling clubs and associations in the upper Thames catchment. The UTFC is entirely funded by its member clubs.
The Cotswold Rivers: characteristics and indications of ecological decline
The most easterly of the Cotswold rivers is the Evenlode. Rising near Moreton in Marsh it flows over a clay catchment in its upper reaches before cutting through the limestone hills between Charlbury and Woodstock, receiving the waters of its principal tributary, the Glyme, after the latter has passed through Blenheim Palace lake.
Evenlode turbidity has worsened steadily in the past 25 years. The Evenlode was the first of the Cotswold rivers to exhibit a decline in its fish populations and loss of macrophytes. Historically, several miles of the Evenlode was run as a trout fishery by the Red Spinner Angling Society, one of Britain’s oldest fishing clubs. The club abandoned attempts to maintain the trout fishery some years ago. An attempt to establish a grayling population with fish from the River Test was a failure. Stocks of coarse fish in the Evenlode have been in decline for a number of years and the river has failed to achieve good ecological status based on its fish populations.
Water quality in the Evenlode is adversely impacted by sewage treatment discharges. Discharges from Moreton in Marsh, Chipping Norton and Milton under Wychwood have all been identified as sources of poor water quality. Church Hanborough spilled 85 times in 2019: 1182 hours recorded.
The Evenlode’s principal tributary is the Glyme. The Glyme has always and only been a trout fishery with few coarse fish present upstream of Woodstock. The Cotswold Flyfishers rents a lengthy stretch upstream of Woodstock. The Glyme too has witnessed worsening turbidity and loss of fly life and in-stream macrophytes (principally ranunculus and starwort). Much more of a pure limestone stream than its Evenlode parent its water quality ought to be excellent, but hasn’t been. Again discharges from sewage treatment works (stws) have been identified as the source of increased phosphate levels. Phosphate stripping has now been agreed for all of the Glyme stws and there is already some evidence of an improvement in water quality.
The best known of the Cotswold rivers, the Windrush has long been noted for the beauty of its valley and its villages and market towns. Bourton on the Water, the Slaughters and the Swells, Burford and Minster Lovell are all well known to Cotswold tourists. The ecological quality of the River Windrush was equally renowned to anglers and naturalists. Twenty-five years ago the Windrush was still a lovely mixed fishery with plentiful stocks of wild brown trout and coarse fish and good grayling numbers in its upper reaches. Water clarity on the lower river was still excellent, though less good on the middle reaches of the river. The river had excellent growth of water crowfoot (ranunculus) and rich fly life as a consequence.
Since then the turbidity which was already beginning to appear below Bourton has spread all the way to the Thames confluence. Grayling have all but disappeared from the river and the biomass of coarse fish and wild brown trout has plummeted. For most of the year the river is now an unpleasant grey colour, only improving after the winterbourne springs have burst and high sustained flows have diluted the polluting inputs.
Once again the principal cause of the problem is not hard to find. Bourton on the Water has discharged untreated sewage for weeks on end and the effluent from smaller works has contributed.
[Witney for spilled for 1395 hours in 2019; Bourton spilled for 1398 hours]
One of the smaller Cotswold rivers, the Leach is less degraded than its larger cousins. Its waters still generally run clear. However, close to its source Northleach stw has become a problem, delivering poor quality effluent and it is probably only a matter of time before the river displays the same indicators of degradation as the nearby Windrush and Coln.
Although the Windrush is the best known of Cotswold rivers, for flyfishermen the Gloucestershire Coln was always the jewel in the crown. Rising on the oolitic limestone close to Cheltenham, the Coln was always noted for the clarity of its water. Frequently mis-described as a chalkstream, the Coln was ranked alongside the Test, Itchen and Kennet as a trout fishery. Its clear waters rich in invertebrates, plant life and trout and grayling, the Coln was a delight to observe and to fish.
While the Coln valley is still a very beautiful part of the Cotswolds, the river has lost its sparkle. It is much more turbid than before and grayling numbers have fallen drastically. At the market town of Fairford it receives repeated does of untreated sewage with the consequence that from Fairford to the Thames the river is highly degraded and is acknowledged as such by the Environment Agency.
Until a couple of years ago the Ampney Brook displayed the characteristics of a pristine trout stream. It ran crystal clear and had good wild trout populations with some coarse fish. Since then deterioration has been rapid and marked with turbidity worsening and fish stocks declining. Ampney St Peter sewage treatment works has repeatedly spilled undiluted sewage.
[Ampney St Peter spilled 90 times in 2019: 1853 hours recorded]
The most westerly of the Cotswold rivers and possibly the last survivor. Like the nearby Ampney Brook, historically the Churn’s principal problem was low flows cause by borehole abstraction. [Thames Water has a number of abstraction licences in this area, taking water from the great and Inferior Oolite beds. These are known to impact variously on flows in the Churn, Ampney Brook and Coln] Although the risk of very low flows (the Churn still dries up in drought years) remains a manifest danger to the river, discharges from CSOs look likely to be the greatest future threat.
Water clarity needs to be a foremost target. Clear unpolluted water is the key to water life. Growing turbidity for all of the Cotswold rivers has been the first sign of sickness.
Species diversity should be another measurable target. The grayling has long been regarded as one of the most sensitive of native species to pollution. Such was the fecundity of grayling in the River Coln, until the 1990s they were netted and removed in large numbers. Today, sadly, the grayling is a rarity almost anywhere in the Cotswolds.
Coarse fish diversity can be just as important an indicator of water quality as wild brown trout. The trout is a winter spawner, when Cotswold water quality is generally at its best. Winter rainfall having nourished the aquifers, filtered calcareous water from the springs dilutes the raw sewage entering the river. However, when flows drop off in the Spring months the grayling and rheophilic coarse fish like the barbel struggle to spawn successfully as algal growth coats the gravel.
Invertebrate and macrophyte diversity and abundance would also be targets we would be looking for. Abundance is as important as diversity. In the past invertebrate surveys have been ticked off approvingly if diversity has been found, but in terms of the ecology of the river just as one swallow doesn’t make a summer, so one ephemerid doesn’t make a hatch! Similarly, such is the robustness of nature that ranunculus will nearly always cling on in the most ideal location, even when its abundance in the river system is only a memory.
The key need is that the plans set clear targets for the reduction of infiltration. It is infiltration of rainwater into the foul sewerage system that provides the justification by the water companies for repeated discharges of untreated sewage. It is evident in the Cotswolds that many sewage treatment works do not have the capacity to serve the populations they are currently meant to serve. Rainwater infiltrating the foul sewerage system then allows the water companies to discharge raw sewage from its CSOs, claiming that its stw is in danger of being overwhelmed. The EA has stated that infiltration is NOT a legal justification for storm discharges, but it is used routinely by the water companies as an excuse for polluting rivers.
Full monitoring and reporting of CSO discharges should be a requirement. Event duration monitors should be present on all CSOs and land treatment areas.
In the Cotswold “tankering” of untreated sewage is widespread. Recently, Thames Water has described some of its tankering operations as “a mistake”. It is not clear in which sense TW meant this, but tankering raw sewage from a works which is failing its consent standards to another works which is “storming” should not be permitted. Water companies should be required to report fully all tankering operations and provide a full explanation for why such emergency measures are necessary and their extent and duration. Otherwise the concern will remain that tankering may be used as a ruse to circumvent discharge standards.