2nd November 2026 River Deben Environment Monitoring Results
We have finally seen increased rainfall after one of Suffolk's driest 6 month periods on record, with one local recorder reporting a 69 day period from mid-June into July and until mid-August where no rain fell at all. River levels dropped and many of our usual sampling sites were dried out. During late September and October we have seen significant changes in rainfall amounts restoring river flow in many places. That said, even with several days of heavy rain in October, we have still not seen river levels return to those expected at this time of year.
Thanks as always to our committed River Deben volunteers who venture out in all weathers to sample and test.
1. E.coli pollution
This month's E.coli results are broadly similar to those reported in October although they were noticeably lower in the section from Easton up to Crettingham, where there is minimal bacterial pollution coupled with clear water (very low turbidity). Lower down the non-tidal Deben, there is a similar picture with the usual exceptions at the Anglian Water STW's at Charsfield and Wickham Market. The Rendlesham STW showed much higher E.coli than for many months - 25,000 colonies per 100ml as against 1,200 to 5,000 in the prior 4 months. This may be due to our sampling coinciding with a peak in the pumped outfall volumes.
In the tidal section, E.coli readings in the section below Woodbridge were minimal but with higher levels witnessed at Melton and Wilford Bridge (around 4,000 colonies per 100ml). The latter are in sharp contrast to those at Ufford (at 200 colonies per 100 ml) which is close to the tidal junction. There is no easy explanation for these variations but there may be an impact from the Melton STW which discharges into the middle of the tidesteam so increasing upstream pollution flow on a rising tide.
The Fynn/Lark section again has the usual hotspots at Henley, Tuddenham and at Martlesham Creek STW's. E.coli levels in this tributary remain stubbornly high due perhaps to low flow and the larger presence of livestock (including equiculture).
At Debenham, there were many fewer dry sites with some evidence of higher E.coli levels than in previous months. Rainfall and water flowing through previously dry sites may be one reason for the elevated levels. However, it is still noticeable that the Debenham STW outfall is much less polluted with E.coli bacteria than any others in the local Anglian Water network.
2. Phosphate pollution
Across the non-tidal Deben phosphate levels are similar to previous months in spite of higher rainfall; there seems no evidence that there is any impact from increased agricultural run-off or from ditches being flushed out. This is especially true in the Crettingham to Wickham Market section where phosphate levels are actually lower than in the two prior months. Even at the Charsfield STW outfall the phosphate level is about a third of those in previous months, signalling perhaps that Anglian Water now have the phosphate removal process under control again.
Perhaps the most encouraging number is that at the Rendlesham STW outfall where the recent phosphate removal investment has led to a more than 10-fold decrease in pollution (from around 5 to 10 mg/ litre at the start of 2026 down to 0.30 mg/litre now). The impact downstream at Ufford has seen reductions in phosphate to bring this area within the "healthy river" goal for the first time in many months.
Phosphate levels in the tidal estuary around Melton/ Woodbridge are, by contrast, rather higher than at the tidal junction, probably due to the fact that there has been no investment in PO4 removal at either Melton or Martlesham Creek. Lower down, tidal washout reduces phosphate very significantly.
For the Fynn/Lark section. the Anglian Water STW hotspots appear to be a more major contributor to the higher phosphate levels than in the rest of the Deben catchment. One of our volunteers from Tuddenham has taken this up with Anglian Water directly requesting explanation and asking for action to invest in what is a simple removal technology; we hope that this with our data and wider public concern will prompt a response.
At Debenham, phosphate readings were higher than those downstream but still similar to or lower than in previous months. There appears to have been minimal impact from the increased rainfall that we have seen with no increase in turbidity locally. The local STW outfall continues to be well within its Environment Agency permitted 0.5 mg/ litre and there are no red-rated sampling sites in the area.
3. Nitrate pollution
Nitrates and phosphates both contribute to algal and weed growth with nitrates often seen as coming from farm run-off and ditch flushing. At this time of year, farmers do apply some fertiliser to winter crops but our data suggests that there is no appreciable effect on nitrate levels in the river. The main hotspots for nitrate pollution continue to be at or downstream from the Anglian Water STW's.
We are reviewing our nitrate testing methods at present thanks to the generous loan of a more sophisticated test meter from the Upper Deben Farm Cluster; our initial comparison tests suggest that we may have been over-reading nitrate levels using the nitrate strip colour comparison method. There will be more on this next month or sooner as we dive deeper into the nitrate testing.
4. Ammonia
The presence of ammonia is most often associated with treated or untreated sewage pollution in our rivers. Hence our findings equate to the main sources of E.coli and of raised electrical conductivity. Almost all the Anglian Water STW outfalls show significant traces of ammonia (above 1.0 mg/ml) and even 100 to 500 metres downstream we have found elevated levels. Martlesham Creek outfall is again the worst performer with 11.8 mg/ml - this level will be toxic to aquatic life; the STW's at Henley and Tuddenham are not far behind.
Full details of ammonia levels over the past few months are in the attached Lab Results folder.
5. Deben Climate Centre in the News
This week saw the publication of the Government's report on water company performance. Anglian Water was rated "requires improvement" for the fifth year in a row, with it being accused of "not taking pollution seriously". DCC were approached for comment in the following BBC article: https://www.bbc.co.uk/news/articles/ckpdg7eq288go
Comments