6th July 2026 River Deben Environment Monitoring Results

This report is based on sampling conducted between 27th June and 6th July across the Deben catchment. After weeks without any significant rainfall and with two recent heat waves, river levels remain at a low level with many dry sample points. Anglian Water issued a domestic hosepipe ban at the end of last week which signals a growing crisis for our rivers and particularly for farmers reliant on abstraction from the Deben to fill their reservoirs.

1. E.coli

Results for bacterial pollution in the non-tidal Deben and its tributaries was broadly similar to the levels found in June but with some notable exceptions.

At Debenham, results were significantly higher than in June with two E.coli spikes - one very large just upstream from the Anglian Water Sewage Treatment Works (STW) and a smaller one in the source streams near Aspall. At 586 colonies per 1ml (the Environment Agency "Safe Bathing" limit is 9 colonies per 1ml), there appears to have been a pollution incident close to the STW sampling site; this may be a one-off incident as a retest later in the week found minimal E.coli present. Nonetheless, the Environment Agency were informed.

The Fynn/Lark numbers showed a significant increase at the River Lark sampling sites and at the Tuddenham downstream sampling point, both perhaps due to lower flow in the river. We are also exploring local ditches at Playford and sites closer to the Tuddenham STW as these indicate raised levels of E.coli; the Playford sampling site is close to private outfalls from a number of off-mains drainage properties - more on this next month...

By contrast in the tidal section, there was clear evidence of a serious pollution incident with very high levels of E.coli pollution from Woodbridge down towards Waldringfield and the mouth of the Deben at Bawdsey. E.coli levels close to Woodbridge Station (92), at Deben Yacht Club (28) and at Kyson Point all (65) peaked at a similar level to those seen in July 2025. The Waldringfield sampling point result was again above the "safe bathing limit" for the second month. The pollution source is unclear but it may be significant that Martlesham Creek STW E.coli was around 2500 colonies per 1ml (higher than any previous reading) and that Anglian Water recorded a Combined Sewer Overflow (CSO) release earlier on 6th July, albeit at 0 minutes. This suggests that the Martlesham Creek STW may be the source. The Environment Agency were informed and our local contact there has been alerted to the potential Waldringfield permit breach.

In addition, the recently added site at the Anglian Water STW at Kirton showed a very high E.coli level and there was a corresponding spike just below the tidal sluice at Falkenham Creek.

2. Phosphate

The picture for July is fairly similar as with almost no rainfall and low river levels, any run-off from agricultural sources in the past weeks is likely to have been minimal. Hence the major source of pollution tends to be from Anglian Water STWs and any private outfalls which are emitting pollutants.

The most notable feature is the dramatic fall over the past 6 to 8 weeks in the Rendlesham STW outfall phosphate level. This has reduced from 7.42 mg/litre in early May down to 0.33 mg/litre in July. The over twenty-fold reduction is entirely due to the commissioning of the phosphate removal technology by Anglian Water (AWS). Both the landowner and Deben Climate Centre are pleased to see this installation which followed discussions with AWS in mid-2025.

At the new Kirton STW sampling point we recorded a very high phosphate reading at 11.41 mg/litre; this is over 100 times the 0.1 mg/litre "healthy river" guideline. There is a strong case for phosphate removal investment here, as there is at the most polluting sites on the Fynn and Lark.

3. Nitrate

As in previous months, nitrate pollution is highest at and downstream from the Anglian Water STW's with almost all sampling points showing nitrate levels at or below 30 ppm.  It is expected that these levels with remain similar until we have significant rainfall as we suspect that nitrates are being held in ditches and smaller dry streams.

4. Ammonia

This month we have continued to use ammonia test strips for measuring levels of ammonia pollution. The data indicates that outside the Anglian Water STW's, ammonia levels are low with a couple of exceptions in the Brandeston and Earl Soham areas.

Based on our experience and the past three months analysis , we are not satisfied with the quality of our results and reliability of this test method. We plan to revert to use of the Hanna Ammonia MR tests in future months to obtain a clearer picture.

5. Dissolved Oxygen

We acquired two more DO2 meters this month which have allowed better coverage of the levels of dissolved oxygen across the Deben catchment. Dissolved Oxygen is a critical parameter to measure as low levels indicate dangers to aquatic life; the following concentrations are a broad guideline:

• Above 5 mg/L: Optimal conditions that support a healthy and diverse fish population.

• 3 to 5 mg/L: Hypoxic/stressful levels; bottom-feeding and sensitive species begin to decline.

• Below 3 mg/L: Lethal to most fish species

  
  

From the River Deben catchment, all tidal and non-tidal sections are healthy and measure at or above 5mg/litre but with one exception. This is in the Brandeston where DO2 levels in the Earl Soham watercourse and at Crettingham are below the optimal level. The Earl Soham Bridge site is the most concerning as this is below the 3 mg/litre level; we have noticed more turbid water and occasional oil pollution at this site over the past 12 months.

Thanks as ever to our committed volunteers for their sampling and testing work this month. We hope to provide an update on the Woodbridge/Waldringfield pollution incidents and other issues which have been flagged with the Environment Agency.

Check out our River Deben Water Quality Dashboard for detailed results by

location.